Explain what this code does. Then, convert this recursive function to an iterative one, making explicit the cubic work that's being done. The functions should return exactly the same output but the iterative one should be faster. Call your function `solve_iterative` and match the type signature of the original function. @lru_cache(maxsize=None) def solve_dp(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: value = min(value, solve_dp(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: sub, how = solve_dp(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) return value
Explain what this code does. Then, convert this recursive function to an iterative one, making explicit the cubic work that's being done. The functions should return exactly the same output but the iterative one should be faster. Call your function `solve_iterative` and match the type signature of the original function. @lru_cache(maxsize=None) def solve_dp(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: value = min(value, solve_dp(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: sub, how = solve_dp(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) return value
This code defines a recursive function `solve_dp` that takes in a list `graph` representing a graph, an integer `lines_left` representing the number of lines remaining to be placed on the graph, and an integer `distance_since_last` representing the distance since the last line was placed. The function returns a tuple containing two elements: the minimum cost of placing the remaining lines on the graph, and the order in which the lines should be placed to achieve this minimum cost. The function uses dynamic programming to memoize the results of subproblems, which helps to avoid redundant computation and improve the performance of the algorithm. The base cases for the recursion are when the length of the graph is less than the number of lines remaining, in which case the cost is set to a large value of `1e9`, and when the number of lines remaining is zero and the length of the graph is also zero, in which case the cost is set to zero. For each recursive call, the function considers two options: (1) not taking the current line, and (2) taking the current line. For option (1), the function simply recurses on the remaining graph and lines, and updates the minimum cost if the current cost is higher than the cost of not taking the current line. For option (2), the function recurses on the remaining graph and lines, but with one fewer line remaining. It then adds the cost of the current line and the cost of any penalty for placing the line too close to the previous line, and updates the minimum cost if the current cost is higher than the cost of taking the current line. To convert this recursive function to an iterative one, we can use a stack to keep track of the state of the recursion and avoid redundant computation. Here is one possible implementation of the iterative function:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | def solve_iterative(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # Initialize the stack and the minimum cost stack = [(graph, lines_left, distance_since_last, (1e9, []))] min_cost = (1e9, []) # Iterate until the stack is empty while stack: graph, lines_left, distance_since_last, (cost, order) = stack.pop() # Option 1: don't take the line if distance_since_last < 10: new_cost, new_order = solve_iterative(graph[1:], lines_left, distance_since_last+1) if new_cost < cost: stack.append((graph, lines_left, distance_since_last, (new_cost, new_order))) min_cost = (new_cost, new_order) # Option 2: take the line if lines_left > 0: new_cost, new_order = solve_iterative(graph[1:], lines_left-1, 0) new_cost += graph[0] + (distance_since_last-8)**2 if new_cost < cost: stack.append((graph, lines_left, distance_since_last, (new_cost, new_order + [len(graph)]))) min_cost = (new_cost, new_order + [len(graph)]) return min_cost |
1 2 3 4 5 6 7 8 9 10 11 12 | def solve_iterative(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [], 0 if lines_left == 0 and len(graph) == 0: return 0, [], 0 # Initialize the stack and the minimum cost stack = [(graph, lines_left, distance_since_last, (1e9, []))] min_cost = (1e9, []) num_updates = 0 # Iterate until the stack is empty while stack: graph, lines_left, distance_since_last, (cost, order |
I extracted the following code from that output:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | def solve_iterative(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # Initialize the stack and the minimum cost stack = [(graph, lines_left, distance_since_last, (1e9, []))] min_cost = (1e9, []) # Iterate until the stack is empty while stack: graph, lines_left, distance_since_last, (cost, order) = stack.pop() # Option 1: don't take the line if distance_since_last < 10: new_cost, new_order = solve_iterative(graph[1:], lines_left, distance_since_last+1) if new_cost < cost: stack.append((graph, lines_left, distance_since_last, (new_cost, new_order))) min_cost = (new_cost, new_order) # Option 2: take the line if lines_left > 0: new_cost, new_order = solve_iterative(graph[1:], lines_left-1, 0) new_cost += graph[0] + (distance_since_last-8)**2 if new_cost < cost: stack.append((graph, lines_left, distance_since_last, (new_cost, new_order + [len(graph)]))) min_cost = (new_cost, new_order + [len(graph)]) return min_cost |
Running the following program:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 | def solve_iterative(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # Initialize the stack and the minimum cost stack = [(graph, lines_left, distance_since_last, (1e9, []))] min_cost = (1e9, []) # Iterate until the stack is empty while stack: graph, lines_left, distance_since_last, (cost, order) = stack.pop() # Option 1: don't take the line if distance_since_last < 10: new_cost, new_order = solve_iterative(graph[1:], lines_left, distance_since_last+1) if new_cost < cost: stack.append((graph, lines_left, distance_since_last, (new_cost, new_order))) min_cost = (new_cost, new_order) # Option 2: take the line if lines_left > 0: new_cost, new_order = solve_iterative(graph[1:], lines_left-1, 0) new_cost += graph[0] + (distance_since_last-8)**2 if new_cost < cost: stack.append((graph, lines_left, distance_since_last, (new_cost, new_order + [len(graph)]))) min_cost = (new_cost, new_order + [len(graph)]) return min_cost answer = 0 import random mylist = list(range(100)) random.shuffle(mylist) from functools import lru_cache @lru_cache(maxsize=None) def my_solve_dp(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: value = min(value, my_solve_dp(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: sub, how = my_solve_dp(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) return value answer = solve_iterative(tuple(mylist), len(mylist)//8, 4) expected = my_solve_dp(tuple(mylist), len(mylist)//8, 4) assert answer == expected, f'Wrong answer; got {answer} instead of {expected}' print('All tests passed') |
Timeout: function took too long to complete
Testing if the previous output contains the string All tests passed
: False
Resulting in output: False
Explain what this code does. Then, convert this recursive function to an iterative one, making explicit the cubic work that's being done. The functions should return exactly the same output but the iterative one should be faster. Call your function `solve_iterative` and match the type signature of the original function. @lru_cache(maxsize=None) def solve_dp(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: value = min(value, solve_dp(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: sub, how = solve_dp(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) return value
Explain what this code does. Then, convert this recursive function to an iterative one, making explicit the cubic work that's being done. The functions should return exactly the same output but the iterative one should be faster. Call your function `solve_iterative` and match the type signature of the original function. @lru_cache(maxsize=None) def solve_dp(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: value = min(value, solve_dp(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: sub, how = solve_dp(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) return value
This code defines a memoized recursive function called `solve_dp` that takes in three arguments: a `graph` (a list of numbers), `lines_left` (an integer representing the number of lines remaining to be processed), and `distance_since_last` (an integer representing the distance since the last line was taken). The function returns a tuple containing the minimum cost and the indices of the lines that were taken to achieve that cost. The function first checks if the number of lines remaining is less than the length of the graph, and if so, it returns a tuple containing a large number (1e9) and an empty list to indicate that it is not possible to process any more lines. If there are no lines remaining and the graph is empty, the function returns a tuple containing 0 and an empty list to indicate that the minimum cost is 0 and no lines were taken. The function then considers two options: not taking the current line and taking the current line. If the current line is not taken, the function recursively calls itself with the graph starting at the second element, the same number of lines remaining, and the distance since the last line was taken incremented by 1. If the distance since the last line was taken is less than 10, this option is considered. If the current line is taken, the function recursively calls itself with the graph starting at the second element, one fewer line remaining, and the distance since the last line was taken reset to 0. The cost of taking the current line is then calculated as the cost of the subproblem plus the value of the current line plus the square of the difference between the distance since the last line was taken and 8. The function finally returns the minimum cost and the indices of the lines that were taken to achieve that cost. To convert this recursive function to an iterative one, we can use a stack to keep track of the state of the function as it progresses. We can also use a dictionary to store the memoized values, as we did in the original function. Here is the iterative version of the function:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 | def solve_iterative(graph, lines_left, distance_since_last): # initialize the stack and the memo dictionary stack = [(graph, lines_left, distance_since_last)] memo = {} # loop until the stack is empty while stack: # pop the top element from the stack graph, lines_left, distance_since_last = stack.pop() # check if the memoized value exists if (len(graph), lines_left, distance_since_last) in memo: # return the memoized value return memo[(len(graph), lines_left, distance_since_last)] # base cases if len(graph) < lines_left: value = (1e9, []) elif lines_left == 0 and len(graph) == 0: value = (0, []) else: # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: stack.append((graph[1:], lines_left, distance_since_last+1)) value = min(value, solve_iterative(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: stack.append((graph[1:], lines_left-1, 0)) sub, how = solve_iterative(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) # store the memoized value memo[(len(graph), lines_left, distance_since_last)] = value # return the memoized value return value |
I extracted the following code from that output:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 | def solve_iterative(graph, lines_left, distance_since_last): # initialize the stack and the memo dictionary stack = [(graph, lines_left, distance_since_last)] memo = {} # loop until the stack is empty while stack: # pop the top element from the stack graph, lines_left, distance_since_last = stack.pop() # check if the memoized value exists if (len(graph), lines_left, distance_since_last) in memo: # return the memoized value return memo[(len(graph), lines_left, distance_since_last)] # base cases if len(graph) < lines_left: value = (1e9, []) elif lines_left == 0 and len(graph) == 0: value = (0, []) else: # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: stack.append((graph[1:], lines_left, distance_since_last+1)) value = min(value, solve_iterative(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: stack.append((graph[1:], lines_left-1, 0)) sub, how = solve_iterative(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) # store the memoized value memo[(len(graph), lines_left, distance_since_last)] = value # return the memoized value return value |
Running the following program:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 | def solve_iterative(graph, lines_left, distance_since_last): # initialize the stack and the memo dictionary stack = [(graph, lines_left, distance_since_last)] memo = {} # loop until the stack is empty while stack: # pop the top element from the stack graph, lines_left, distance_since_last = stack.pop() # check if the memoized value exists if (len(graph), lines_left, distance_since_last) in memo: # return the memoized value return memo[(len(graph), lines_left, distance_since_last)] # base cases if len(graph) < lines_left: value = (1e9, []) elif lines_left == 0 and len(graph) == 0: value = (0, []) else: # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: stack.append((graph[1:], lines_left, distance_since_last+1)) value = min(value, solve_iterative(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: stack.append((graph[1:], lines_left-1, 0)) sub, how = solve_iterative(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) # store the memoized value memo[(len(graph), lines_left, distance_since_last)] = value # return the memoized value return value answer = 0 import random mylist = list(range(100)) random.shuffle(mylist) from functools import lru_cache @lru_cache(maxsize=None) def my_solve_dp(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: value = min(value, my_solve_dp(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: sub, how = my_solve_dp(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) return value answer = solve_iterative(tuple(mylist), len(mylist)//8, 4) expected = my_solve_dp(tuple(mylist), len(mylist)//8, 4) assert answer == expected, f'Wrong answer; got {answer} instead of {expected}' print('All tests passed') |
Timeout: function took too long to complete
Testing if the previous output contains the string All tests passed
: False
Resulting in output: False
Explain what this code does. Then, convert this recursive function to an iterative one, making explicit the cubic work that's being done. The functions should return exactly the same output but the iterative one should be faster. Call your function `solve_iterative` and match the type signature of the original function. @lru_cache(maxsize=None) def solve_dp(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: value = min(value, solve_dp(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: sub, how = solve_dp(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) return value
Explain what this code does. Then, convert this recursive function to an iterative one, making explicit the cubic work that's being done. The functions should return exactly the same output but the iterative one should be faster. Call your function `solve_iterative` and match the type signature of the original function. @lru_cache(maxsize=None) def solve_dp(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: value = min(value, solve_dp(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: sub, how = solve_dp(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) return value
This function `solve_dp` is a recursive dynamic programming (DP) solution to a problem related to a graph. The function takes in three arguments: `graph`, `lines_left`, and `distance_since_last`. The `graph` is a list of values representing the graph, `lines_left` is an integer representing the number of lines that can be taken, and `distance_since_last` is an integer representing the distance since the last line was taken. The function returns a tuple containing two values: the minimum cost and the list of indices of the lines taken to achieve that minimum cost. The base cases for the recursion are when the length of the graph is less than the number of lines left and when there are no lines left and the length of the graph is zero. In the first case, the function returns a tuple containing a large number (1e9) and an empty list. In the second case, the function returns a tuple containing zero and an empty list. The function considers two options at each step: taking a line or not taking a line. If the distance since the last line was taken is less than 10, the function considers not taking a line by recursively calling the function with the graph starting at the second element, the same number of lines left, and the distance since the last line was taken incremented by 1. If there are still lines left, the function also considers taking a line by recursively calling the function with the graph starting at the second element, one less line left, and the distance since the last line was taken reset to 0. The cost of taking the line is calculated by adding the value of the first element in the graph to the square of the difference between the distance since the last line was taken and 8. The function then returns the minimum cost and the list of indices of the lines taken to achieve that minimum cost. To convert this function to an iterative one, we can use a stack to keep track of the state of the recursion. Here's an example of how the function can be implemented iteratively:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | def solve_iterative(graph, lines_left): stack = [(1e9, [], graph[1:], lines_left, graph[0])] while stack: (cost, how, graph, lines_left, distance_since_last) = stack.pop() if len(graph) < lines_left: continue if lines_left == 0 and len(graph) == 0: return cost, how # option 1: don't take the line if distance_since_last < 10: stack.append((cost, how, graph[1:], lines_left, distance_since_last+1)) cost = min(cost, solve_iterative(graph[1:], lines_left)[0]) # option 2: take the line if lines_left > 0: sub, how = solve_iterative(graph[1:], lines_left-1) new_cost = sub + graph[0] + (distance_since_last-8)**2 stack.append((new_cost, how + [len(graph)-1], graph[1:], lines_left-1, 0)) cost = min(cost, new_cost) return cost, how |
I extracted the following code from that output:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | def solve_iterative(graph, lines_left): stack = [(1e9, [], graph[1:], lines_left, graph[0])] while stack: (cost, how, graph, lines_left, distance_since_last) = stack.pop() if len(graph) < lines_left: continue if lines_left == 0 and len(graph) == 0: return cost, how # option 1: don't take the line if distance_since_last < 10: stack.append((cost, how, graph[1:], lines_left, distance_since_last+1)) cost = min(cost, solve_iterative(graph[1:], lines_left)[0]) # option 2: take the line if lines_left > 0: sub, how = solve_iterative(graph[1:], lines_left-1) new_cost = sub + graph[0] + (distance_since_last-8)**2 stack.append((new_cost, how + [len(graph)-1], graph[1:], lines_left-1, 0)) cost = min(cost, new_cost) return cost, how |
Running the following program:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 | def solve_iterative(graph, lines_left): stack = [(1e9, [], graph[1:], lines_left, graph[0])] while stack: (cost, how, graph, lines_left, distance_since_last) = stack.pop() if len(graph) < lines_left: continue if lines_left == 0 and len(graph) == 0: return cost, how # option 1: don't take the line if distance_since_last < 10: stack.append((cost, how, graph[1:], lines_left, distance_since_last+1)) cost = min(cost, solve_iterative(graph[1:], lines_left)[0]) # option 2: take the line if lines_left > 0: sub, how = solve_iterative(graph[1:], lines_left-1) new_cost = sub + graph[0] + (distance_since_last-8)**2 stack.append((new_cost, how + [len(graph)-1], graph[1:], lines_left-1, 0)) cost = min(cost, new_cost) return cost, how answer = 0 import random mylist = list(range(100)) random.shuffle(mylist) from functools import lru_cache @lru_cache(maxsize=None) def my_solve_dp(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: value = min(value, my_solve_dp(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: sub, how = my_solve_dp(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) return value answer = solve_iterative(tuple(mylist), len(mylist)//8, 4) expected = my_solve_dp(tuple(mylist), len(mylist)//8, 4) assert answer == expected, f'Wrong answer; got {answer} instead of {expected}' print('All tests passed') |
Traceback (most recent call last):
File "/usr/src/app/main.py", line 53, in <module>
answer = solve_iterative(tuple(mylist), len(mylist)//8, 4)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: solve_iterative() takes 2 positional arguments but 3 were given
Testing if the previous output contains the string All tests passed
: False
Resulting in output: False
Explain what this code does. Then, convert this recursive function to an iterative one, making explicit the cubic work that's being done. The functions should return exactly the same output but the iterative one should be faster. Call your function `solve_iterative` and match the type signature of the original function. @lru_cache(maxsize=None) def solve_dp(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: value = min(value, solve_dp(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: sub, how = solve_dp(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) return value
Explain what this code does. Then, convert this recursive function to an iterative one, making explicit the cubic work that's being done. The functions should return exactly the same output but the iterative one should be faster. Call your function `solve_iterative` and match the type signature of the original function. @lru_cache(maxsize=None) def solve_dp(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: value = min(value, solve_dp(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: sub, how = solve_dp(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) return value
This code defines a recursive function `solve_dp` that takes in three arguments: a list of integers `graph`, an integer `lines_left`, and an integer `distance_since_last`. The function calculates the minimum total cost of "taking" a certain number of lines from the `graph` list, where the cost of taking a line is its value plus the square of the difference between its position in the list and the position of the line taken before it. The function uses dynamic programming and memoization to avoid unnecessary computation. The function returns a tuple containing the minimum total cost and a list of the indices of the lines that were taken to achieve that cost. If it is not possible to take the required number of lines, the function returns a tuple containing a large number (`1e9`) and an empty list. To convert this function to an iterative one, we can use a stack to keep track of the function calls and their arguments. We will also need to store the memoized values in a dictionary, since we no longer have the `@lru_cache` decorator to do that for us. Here's the iterative version of the function:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | def solve_iterative(graph, lines_left, distance_since_last): memo = {} stack = [(graph, lines_left, distance_since_last)] while stack: graph, lines_left, distance_since_last = stack.pop() key = (len(graph), lines_left, distance_since_last) if key in memo: continue if len(graph) < lines_left: value = 1e9, [] elif lines_left == 0 and len(graph) == 0: value = 0, [] else: # option 1: don't take the line value = 1e9, [] if distance_since_last < 10: stack.append((graph[1:], lines_left, distance_since_last+1)) value = min(value, memo[key]) # option 2: take the line if lines_left > 0: stack.append((graph[1:], lines_left-1, 0)) sub, how = memo[key] sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) memo[key] = value return memo[(len(graph), lines_left, distance_since_last)] |
I extracted the following code from that output:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | def solve_iterative(graph, lines_left, distance_since_last): memo = {} stack = [(graph, lines_left, distance_since_last)] while stack: graph, lines_left, distance_since_last = stack.pop() key = (len(graph), lines_left, distance_since_last) if key in memo: continue if len(graph) < lines_left: value = 1e9, [] elif lines_left == 0 and len(graph) == 0: value = 0, [] else: # option 1: don't take the line value = 1e9, [] if distance_since_last < 10: stack.append((graph[1:], lines_left, distance_since_last+1)) value = min(value, memo[key]) # option 2: take the line if lines_left > 0: stack.append((graph[1:], lines_left-1, 0)) sub, how = memo[key] sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) memo[key] = value return memo[(len(graph), lines_left, distance_since_last)] |
Running the following program:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 | def solve_iterative(graph, lines_left, distance_since_last): memo = {} stack = [(graph, lines_left, distance_since_last)] while stack: graph, lines_left, distance_since_last = stack.pop() key = (len(graph), lines_left, distance_since_last) if key in memo: continue if len(graph) < lines_left: value = 1e9, [] elif lines_left == 0 and len(graph) == 0: value = 0, [] else: # option 1: don't take the line value = 1e9, [] if distance_since_last < 10: stack.append((graph[1:], lines_left, distance_since_last+1)) value = min(value, memo[key]) # option 2: take the line if lines_left > 0: stack.append((graph[1:], lines_left-1, 0)) sub, how = memo[key] sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) memo[key] = value return memo[(len(graph), lines_left, distance_since_last)] answer = 0 import random mylist = list(range(100)) random.shuffle(mylist) from functools import lru_cache @lru_cache(maxsize=None) def my_solve_dp(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: value = min(value, my_solve_dp(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: sub, how = my_solve_dp(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) return value answer = solve_iterative(tuple(mylist), len(mylist)//8, 4) expected = my_solve_dp(tuple(mylist), len(mylist)//8, 4) assert answer == expected, f'Wrong answer; got {answer} instead of {expected}' print('All tests passed') |
Traceback (most recent call last):
File "/usr/src/app/main.py", line 60, in <module>
answer = solve_iterative(tuple(mylist), len(mylist)//8, 4)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/src/app/main.py", line 19, in solve_iterative
value = min(value, memo[key])
~~~~^^^^^
KeyError: (100, 12, 4)
Testing if the previous output contains the string All tests passed
: False
Resulting in output: True
Explain what this code does. Then, convert this recursive function to an iterative one, making explicit the cubic work that's being done. The functions should return exactly the same output but the iterative one should be faster. Call your function `solve_iterative` and match the type signature of the original function. @lru_cache(maxsize=None) def solve_dp(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: value = min(value, solve_dp(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: sub, how = solve_dp(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) return value
Explain what this code does. Then, convert this recursive function to an iterative one, making explicit the cubic work that's being done. The functions should return exactly the same output but the iterative one should be faster. Call your function `solve_iterative` and match the type signature of the original function. @lru_cache(maxsize=None) def solve_dp(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: value = min(value, solve_dp(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: sub, how = solve_dp(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) return value
The given code defines a function `solve_dp` that takes in three parameters: 1. `graph`: a list of integers representing the lengths of lines in a grid. 2. `lines_left`: an integer representing the number of lines that can still be taken from the grid. 3. `distance_since_last`: an integer representing the distance since the last line was taken. The function uses dynamic programming (DP) to find the minimum total cost of taking a certain number of lines from the grid, while also keeping track of the indices of the lines that were taken. The cost of taking a line is the square of the difference between its length and the length of the previous line taken, minus 8. The function has a base case where it returns a large value (1e9) if there are more lines left to take than there are lines in the graph. It also has a base case where it returns 0 and an empty list if there are no lines left to take and the graph is empty. If neither of these base cases are met, the function considers two options: 1. Don't take the current line. In this case, the function recursively calls itself with the graph minus the first element, the same number of lines left, and an incremented distance since the last line was taken. 2. Take the current line. In this case, the function recursively calls itself with the graph minus the first element, one fewer line left to take, and a reset distance since the last line was taken. It then adds the cost of taking the current line to the minimum cost returned by the recursive call. The function returns the minimum cost and the list of indices of the lines taken. To convert this recursive function to an iterative one, we can use a stack to keep track of the function calls. We can also use an explicit loop to simulate the recursive calls. Here's one possible implementation of an iterative version of the function:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | def solve_iterative(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] stack = [(graph, lines_left, distance_since_last)] min_cost = (1e9, []) while stack: graph, lines_left, distance_since_last = stack.pop() if distance_since_last < 10: stack.append((graph[1:], lines_left, distance_since_last+1)) if lines_left > 0: stack.append((graph[1:], lines_left-1, 0)) sub, how = solve_iterative(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 min_cost = min(min_cost, (sub, how + [len(graph)])) return min_cost |
I extracted the following code from that output:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | def solve_iterative(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] stack = [(graph, lines_left, distance_since_last)] min_cost = (1e9, []) while stack: graph, lines_left, distance_since_last = stack.pop() if distance_since_last < 10: stack.append((graph[1:], lines_left, distance_since_last+1)) if lines_left > 0: stack.append((graph[1:], lines_left-1, 0)) sub, how = solve_iterative(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 min_cost = min(min_cost, (sub, how + [len(graph)])) return min_cost |
Running the following program:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 | def solve_iterative(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] stack = [(graph, lines_left, distance_since_last)] min_cost = (1e9, []) while stack: graph, lines_left, distance_since_last = stack.pop() if distance_since_last < 10: stack.append((graph[1:], lines_left, distance_since_last+1)) if lines_left > 0: stack.append((graph[1:], lines_left-1, 0)) sub, how = solve_iterative(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 min_cost = min(min_cost, (sub, how + [len(graph)])) return min_cost answer = 0 import random mylist = list(range(100)) random.shuffle(mylist) from functools import lru_cache @lru_cache(maxsize=None) def my_solve_dp(graph, lines_left, distance_since_last): if len(graph) < lines_left: return 1e9, [] if lines_left == 0 and len(graph) == 0: return 0, [] # option 1: don't take the line value = (1e9, []) if distance_since_last < 10: value = min(value, my_solve_dp(graph[1:], lines_left, distance_since_last+1)) # option 2: take the line if lines_left > 0: sub, how = my_solve_dp(graph[1:], lines_left-1, 0) sub += graph[0] + (distance_since_last-8)**2 value = min(value, (sub, how + [len(graph)])) return value answer = solve_iterative(tuple(mylist), len(mylist)//8, 4) expected = my_solve_dp(tuple(mylist), len(mylist)//8, 4) assert answer == expected, f'Wrong answer; got {answer} instead of {expected}' print('All tests passed') |
Traceback (most recent call last):
File "/usr/src/app/main.py", line 53, in <module>
answer = solve_iterative(tuple(mylist), len(mylist)//8, 4)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/src/app/main.py", line 18, in solve_iterative
sub, how = solve_iterative(graph[1:], lines_left-1, 0)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/src/app/main.py", line 18, in solve_iterative
sub, how = solve_iterative(graph[1:], lines_left-1, 0)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/src/app/main.py", line 18, in solve_iterative
sub, how = solve_iterative(graph[1:], lines_left-1, 0)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[Previous line repeated 996 more times]
RecursionError: maximum recursion depth exceeded
Testing if the previous output contains the string All tests passed
: False
Resulting in output: False