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 provided recursive code is a dynamic programming solution for a problem where you're given a graph (represented as a list where each element has some associated cost) and a constraint on how many lines (or elements) you can choose (`lines_left`). Additionally, there's a penalty applied based on the `distance_since_last` line you took, with a specific cost calculation given by `graph[0] + (distance_since_last-8)**2`. The goal is to minimize the total cost while respecting the constraints. The function `solve_dp` computes the minimum cost and the sequence of choices (as a list of indices in the original graph list) to achieve this cost. It does so by exploring two options at each step: 1. Not taking the current line and moving to the next, if the `distance_since_last` is less than 10. 2. Taking the current line, which resets the `distance_since_last` to 0 and decreases the `lines_left` by 1. The use of `@lru_cache` is to memoize the results of previous computations to avoid recalculating the same scenarios, which significantly reduces the total number of computations. ### Conversion to Iterative Function Converting this to an iterative function involves explicitly managing the states that the recursive function implicitly handles via the call stack. We'll use a 3-dimensional DP array, where dimensions represent the length of the graph processed, the `lines_left`, and the `distance_since_last`, respectively. Here's how the conversion might look:
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): n = len(graph) MAX_DIST = 10 INF = int(1e9) # dp[length][lines][distance] = (cost, path) dp = [[[INF, []] for _ in range(MAX_DIST)] for _ in range(lines_left + 1)] for _ in range(n + 1): dp.append([[INF, []] * MAX_DIST for _ in range(lines_left + 1)]) dp[n][0][0] = (0, []) for length in range(n-1, -1, -1): for lines in range(lines_left + 1): for distance in range(MAX_DIST): # option 1: don't take the line if distance + 1 < MAX_DIST: next_value = dp[length + 1][lines][distance + 1] dp[length][lines][distance] = min(dp[length][lines][distance], next_value) # option 2: take the line if lines > 0: sub, how = dp[length + 1][lines - 1][0] sub += graph[length] + (distance - 8) ** 2 new_value = (sub, how + [length + 1]) dp[length][lines][distance] = min(dp[length][lines][distance], new_value) return dp[0][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): n = len(graph) MAX_DIST = 10 INF = int(1e9) # dp[length][lines][distance] = (cost, path) dp = [[[INF, []] for _ in range(MAX_DIST)] for _ in range(lines_left + 1)] for _ in range(n + 1): dp.append([[INF, []] * MAX_DIST for _ in range(lines_left + 1)]) dp[n][0][0] = (0, []) for length in range(n-1, -1, -1): for lines in range(lines_left + 1): for distance in range(MAX_DIST): # option 1: don't take the line if distance + 1 < MAX_DIST: next_value = dp[length + 1][lines][distance + 1] dp[length][lines][distance] = min(dp[length][lines][distance], next_value) # option 2: take the line if lines > 0: sub, how = dp[length + 1][lines - 1][0] sub += graph[length] + (distance - 8) ** 2 new_value = (sub, how + [length + 1]) dp[length][lines][distance] = min(dp[length][lines][distance], new_value) return dp[0][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 63 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) MAX_DIST = 10 INF = int(1e9) # dp[length][lines][distance] = (cost, path) dp = [[[INF, []] for _ in range(MAX_DIST)] for _ in range(lines_left + 1)] for _ in range(n + 1): dp.append([[INF, []] * MAX_DIST for _ in range(lines_left + 1)]) dp[n][0][0] = (0, []) for length in range(n-1, -1, -1): for lines in range(lines_left + 1): for distance in range(MAX_DIST): # option 1: don't take the line if distance + 1 < MAX_DIST: next_value = dp[length + 1][lines][distance + 1] dp[length][lines][distance] = min(dp[length][lines][distance], next_value) # option 2: take the line if lines > 0: sub, how = dp[length + 1][lines - 1][0] sub += graph[length] + (distance - 8) ** 2 new_value = (sub, how + [length + 1]) dp[length][lines][distance] = min(dp[length][lines][distance], new_value) return dp[0][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 61, in <module>
answer = solve_iterative(tuple(mylist), len(mylist)//8, 4)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/src/app/main.py", line 20, in solve_iterative
dp[length][lines][distance] = min(dp[length][lines][distance], next_value)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: '<' not supported between instances of 'list' and 'int'
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 is a dynamic programming solution to a problem where you are given a graph represented as a list, and you need to decide on taking lines (actions) based on the remaining lines you can take (`lines_left`) and the distance since the last line taken (`distance_since_last`). The goal is to minimize a certain cost, which increases based on the distance since the last line taken, with a penalty for distances greater than 8. The function returns the minimum cost and the list of actions (specific indices in the graph) that lead to this cost. Now, let's convert this recursive function to an iterative one. To do this, we'll explicitly manage the states we need to consider, using a dynamic programming table to store the best cost and action sequence for every combination of the current position in the graph, the lines left, and the distance since the last line.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) dp = [[[float('inf'), []] for _ in range(11)] for _ in range(lines_left+1)] for i in range(n+1): dp.append([[float('inf'), []] for _ in range(11)]) dp[i][0][0] = 0, [] for i in range(n-1, -1, -1): for lines in range(lines_left+1): for distance in range(1, 11): # option 1: don't take the line if distance < 10 and i+1 < n: cost, path = dp[lines][distance+1][i+1] if cost < dp[lines][distance][i][0]: dp[lines][distance][i] = cost, path # option 2: take the line if lines > 0 and i+1 < n: cost, path = dp[lines-1][0][i+1] cost += graph[i] + (distance-8)**2 if cost < dp[lines][distance][i][0]: dp[lines][distance][i] = cost, path + [n-i] return dp[lines_left][distance_since_last][0] |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) # Initialize DP table: dp[i][j][k] holds the minimum cost and path for the first i elements, # with j lines left, and k distance since the last line. dp = [[[float('inf'), []] for _ in range(11)] for _ in range(lines_left+1)] for j in range(lines_left+1): dp[j][0] = (0, []) # Base case: no cost and empty path if no distance since the last line. for i in range(1, n+1): for j in range(lines_left+1): for k in range(1, 11): # Don't take the line if k < 10: cost, path = dp[j][k-1] dp[j][k] = min(dp[j][k], (cost, path)) # Take the line if j > 0: cost, path = dp[j-1][0] cost += graph[i-1] + (k-8)**2 dp[j][k] = min(dp[j][k], (cost, path + [i])) # Find the optimal solution starting from the initial conditions. return min(dp[lines_left][1:]) |
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 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) # Initialize DP table: dp[i][j][k] holds the minimum cost and path for the first i elements, # with j lines left, and k distance since the last line. dp = [[[float('inf'), []] for _ in range(11)] for _ in range(lines_left+1)] for j in range(lines_left+1): dp[j][0] = (0, []) # Base case: no cost and empty path if no distance since the last line. for i in range(1, n+1): for j in range(lines_left+1): for k in range(1, 11): # Don't take the line if k < 10: cost, path = dp[j][k-1] dp[j][k] = min(dp[j][k], (cost, path)) # Take the line if j > 0: cost, path = dp[j-1][0] cost += graph[i-1] + (k-8)**2 dp[j][k] = min(dp[j][k], (cost, path + [i])) # Find the optimal solution starting from the initial conditions. return min(dp[lines_left][1:]) |
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 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) # Initialize DP table: dp[i][j][k] holds the minimum cost and path for the first i elements, # with j lines left, and k distance since the last line. dp = [[[float('inf'), []] for _ in range(11)] for _ in range(lines_left+1)] for j in range(lines_left+1): dp[j][0] = (0, []) # Base case: no cost and empty path if no distance since the last line. for i in range(1, n+1): for j in range(lines_left+1): for k in range(1, 11): # Don't take the line if k < 10: cost, path = dp[j][k-1] dp[j][k] = min(dp[j][k], (cost, path)) # Take the line if j > 0: cost, path = dp[j-1][0] cost += graph[i-1] + (k-8)**2 dp[j][k] = min(dp[j][k], (cost, path + [i])) # Find the optimal solution starting from the initial conditions. return min(dp[lines_left][1:]) 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 56, in <module>
answer = solve_iterative(tuple(mylist), len(mylist)//8, 4)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/src/app/main.py", line 16, in solve_iterative
dp[j][k] = min(dp[j][k], (cost, path))
^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: '<' not supported between instances of 'tuple' and 'list'
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 provided recursive function, `solve_dp`, is designed to solve a particular optimization problem. Given a `graph` represented as a list (where each element might represent, for example, the cost of taking a particular action at that step), an integer `lines_left` indicating how many more actions can be taken, and an integer `distance_since_last` indicating the distance (in terms of steps in the list) since the last action was taken, the function returns a tuple. The first element of the tuple is the minimum total cost of taking actions according to the constraints provided by `lines_left` and `distance_since_last`, and the second element is a list of integers that represent the indices in the original list `graph` where actions are taken to achieve this minimum cost. It explores two options at each step: either to "take a line" at the current position (which resets `distance_since_last` to 0 and decreases `lines_left` by 1) or to not take a line (which increments `distance_since_last` by 1 and leaves `lines_left` unchanged). The cost of taking a line at a particular position includes the cost at that position in the `graph` plus a penalty based on the `distance_since_last` (specifically, `(distance_since_last-8)**2`). The challenge here is to convert this recursive function with memoization (`lru_cache`) into an iterative version. Let's proceed with this conversion:
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 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) dp = [[(1e9, []) for _ in range(11)] for _ in range(lines_left + 1)] dp[0][distance_since_last] = (0, []) for i in range(1, n + 1): new_dp = [[(1e9, []) for _ in range(11)] for _ in range(lines_left + 1)] for j in range(lines_left + 1): for k in range(11): # If not taking the line if k < 10: new_value = dp[j][k + 1] new_dp[j][k] = min(new_dp[j][k], new_value) # If taking the line if j > 0 and k <= 10: sub, how = dp[j - 1][0] sub += graph[i - 1] + (k - 8) ** 2 new_value = (sub, how + [i]) new_dp[j][0] = min(new_dp[j][0], new_value) dp = new_dp # Find the best among all possibilities best = (1e9, []) for j in range(lines_left + 1): for k in range(11): best = min(best, dp[j][k]) return best |
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 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) dp = [[(1e9, []) for _ in range(11)] for _ in range(lines_left + 1)] dp[0][distance_since_last] = (0, []) for i in range(1, n + 1): new_dp = [[(1e9, []) for _ in range(11)] for _ in range(lines_left + 1)] for j in range(lines_left + 1): for k in range(11): # If not taking the line if k < 10: new_value = dp[j][k + 1] new_dp[j][k] = min(new_dp[j][k], new_value) # If taking the line if j > 0 and k <= 10: sub, how = dp[j - 1][0] sub += graph[i - 1] + (k - 8) ** 2 new_value = (sub, how + [i]) new_dp[j][0] = min(new_dp[j][0], new_value) dp = new_dp # Find the best among all possibilities best = (1e9, []) for j in range(lines_left + 1): for k in range(11): best = min(best, dp[j][k]) return best |
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 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) dp = [[(1e9, []) for _ in range(11)] for _ in range(lines_left + 1)] dp[0][distance_since_last] = (0, []) for i in range(1, n + 1): new_dp = [[(1e9, []) for _ in range(11)] for _ in range(lines_left + 1)] for j in range(lines_left + 1): for k in range(11): # If not taking the line if k < 10: new_value = dp[j][k + 1] new_dp[j][k] = min(new_dp[j][k], new_value) # If taking the line if j > 0 and k <= 10: sub, how = dp[j - 1][0] sub += graph[i - 1] + (k - 8) ** 2 new_value = (sub, how + [i]) new_dp[j][0] = min(new_dp[j][0], new_value) dp = new_dp # Find the best among all possibilities best = (1e9, []) for j in range(lines_left + 1): for k in range(11): best = min(best, dp[j][k]) return best 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 64, in <module>
assert answer == expected, f'Wrong answer; got {answer} instead of {expected}'
^^^^^^^^^^^^^^^^^^
AssertionError: Wrong answer; got (1000000000.0, []) instead of (182, [6, 15, 21, 31, 40, 49, 60, 67, 75, 85, 93, 99])
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 recursive function you've provided, `solve_dp`, is designed to solve a dynamic programming problem related to choosing points (or "lines") from a graph under certain constraints. Specifically, it aims to minimize a cost function while deciding whether to "take a line" at each step, given a maximum number of lines that can be taken (`lines_left`), and the distance since the last line taken (`distance_since_last`). The cost of taking a line includes the value at the current point in the graph plus a penalty based on how many steps have been taken since the last line was taken. The function uses memoization (`lru_cache`) to avoid recomputing values for the same inputs, enhancing performance for overlapping subproblems. Here's how the recursive function works: 1. **Base Cases**: If the remaining graph is shorter than the number of lines left to take, it returns a high cost (`1e9`) since it's impossible to fulfill the requirement. If there are no more lines left to take and the graph is empty, it returns zero cost and an empty solution path. 2. **Option 1 - Don't Take the Line**: It first considers not taking a line at the current position if doing so wouldn't exceed the maximum allowed distance since the last line was taken. It recursively calls itself with the rest of the graph, keeping the number of lines left and incrementing the distance since the last line. 3. **Option 2 - Take the Line**: If there are lines left to take, it considers taking a line at the current position, resetting the distance since the last line to zero and decrementing the number of lines left. It adds the current graph value and the squared penalty for the distance since the last line to the total cost. 4. **Choosing the Best Option**: It compares the outcomes of taking or not taking the line, choosing the one with the lower cost, and returns the total cost and the solution path up to this point. Now, let's convert this recursive function into an iterative one, `solve_iterative`, making the cubic work explicit. This conversion will involve dynamic programming with tabulation.
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): n = len(graph) dp = [[[1e9, []] for _ in range(11)] for _ in range(lines_left+1)] dp[0][distance_since_last] = [0, []] # Base case: no lines left, specific distance for i in range(1, n+1): for j in range(lines_left+1): for k in range(1, 11): # distance_since_last # Option 1: Don't take the line if k < 10: if dp[j][k][0] < dp[j][k+1][0]: dp[j][k+1] = [dp[j][k][0], dp[j][k][1][:]] # Option 2: Take the line if j > 0: sub = dp[j-1][0][0] + graph[i-1] + (k-8)**2 if sub < dp[j][1][0]: dp[j][1] = [sub, dp[j-1][0][1] + [n-i+1]] # Reconstruct the solution from dp table answer = min(dp[j][1] for j in range(lines_left+1)) return answer # Example usage graph = [3, 2, 5, 1, 8] lines_left = 2 distance_since_last = 1 print(solve_iterative(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): n = len(graph) dp = [[[1e9, []] for _ in range(11)] for _ in range(lines_left+1)] dp[0][distance_since_last] = [0, []] # Base case: no lines left, specific distance for i in range(1, n+1): for j in range(lines_left+1): for k in range(1, 11): # distance_since_last # Option 1: Don't take the line if k < 10: if dp[j][k][0] < dp[j][k+1][0]: dp[j][k+1] = [dp[j][k][0], dp[j][k][1][:]] # Option 2: Take the line if j > 0: sub = dp[j-1][0][0] + graph[i-1] + (k-8)**2 if sub < dp[j][1][0]: dp[j][1] = [sub, dp[j-1][0][1] + [n-i+1]] # Reconstruct the solution from dp table answer = min(dp[j][1] for j in range(lines_left+1)) return answer # Example usage graph = [3, 2, 5, 1, 8] lines_left = 2 distance_since_last = 1 print(solve_iterative(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): n = len(graph) dp = [[[1e9, []] for _ in range(11)] for _ in range(lines_left+1)] dp[0][distance_since_last] = [0, []] # Base case: no lines left, specific distance for i in range(1, n+1): for j in range(lines_left+1): for k in range(1, 11): # distance_since_last # Option 1: Don't take the line if k < 10: if dp[j][k][0] < dp[j][k+1][0]: dp[j][k+1] = [dp[j][k][0], dp[j][k][1][:]] # Option 2: Take the line if j > 0: sub = dp[j-1][0][0] + graph[i-1] + (k-8)**2 if sub < dp[j][1][0]: dp[j][1] = [sub, dp[j-1][0][1] + [n-i+1]] # Reconstruct the solution from dp table answer = min(dp[j][1] for j in range(lines_left+1)) return answer # Example usage graph = [3, 2, 5, 1, 8] lines_left = 2 distance_since_last = 1 print(solve_iterative(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') |
[0, []]
Traceback (most recent call last):
File "/usr/src/app/main.py", line 62, in <module>
assert answer == expected, f'Wrong answer; got {answer} instead of {expected}'
^^^^^^^^^^^^^^^^^^
AssertionError: Wrong answer; got [1000000000.0, []] instead of (163, [3, 10, 20, 29, 40, 48, 58, 66, 76, 86, 93, 100])
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 recursive code is designed to solve a problem where you have a graph (in this case, a simple list) that represents some metric (e.g., cost, distance) at each step, and you are trying to find the minimum cost way to traverse this graph using a given number of "lines" (actions, steps, etc.). After each line, you can choose to continue without taking another line, but there's an increasing cost associated with the distance since the last line was taken, specifically if this distance is less than 10. The cost of taking a line includes the graph's current node value plus a penalty based on the distance since the last line was taken (the penalty is quadratic, `(distance_since_last-8)**2`). The function returns a tuple containing the minimum cost to traverse the graph under these conditions and the list of indices at which lines were taken. Now, let’s convert this recursive function into an iterative one for efficiency. We will use dynamic programming to explicitly handle the problem iteratively, which should avoid the overhead of recursion and make the cubic work more apparent.
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 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) dp = [[[1e9, []] for _ in range(11)] for _ in range(lines_left+1)] dp[0][distance_since_last][0] = 0 # Base case for i in range(1, n+1): for j in range(lines_left+1): for k in range(11): # If we don't take the line if k < 10: next_cost, next_how = dp[j][k+1] if dp[j][k][0] < next_cost: dp[j][k+1] = dp[j][k] else: dp[j][k+1] = [dp[j][k][0], dp[j][k][1][:]] # If we take the line if j > 0: sub, how = dp[j-1][0] sub += graph[i-1] + (k-8)**2 if sub < dp[j][0][0]: dp[j][0] = [sub, how + [i]] # Find the minimum cost and its corresponding path min_cost, path = min((dp[lines_left][k][0], dp[lines_left][k][1]) for k in range(11)) return min_cost, path |
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 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) dp = [[[1e9, []] for _ in range(11)] for _ in range(lines_left+1)] dp[0][distance_since_last][0] = 0 # Base case for i in range(1, n+1): for j in range(lines_left+1): for k in range(11): # If we don't take the line if k < 10: next_cost, next_how = dp[j][k+1] if dp[j][k][0] < next_cost: dp[j][k+1] = dp[j][k] else: dp[j][k+1] = [dp[j][k][0], dp[j][k][1][:]] # If we take the line if j > 0: sub, how = dp[j-1][0] sub += graph[i-1] + (k-8)**2 if sub < dp[j][0][0]: dp[j][0] = [sub, how + [i]] # Find the minimum cost and its corresponding path min_cost, path = min((dp[lines_left][k][0], dp[lines_left][k][1]) for k in range(11)) return min_cost, path |
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 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) dp = [[[1e9, []] for _ in range(11)] for _ in range(lines_left+1)] dp[0][distance_since_last][0] = 0 # Base case for i in range(1, n+1): for j in range(lines_left+1): for k in range(11): # If we don't take the line if k < 10: next_cost, next_how = dp[j][k+1] if dp[j][k][0] < next_cost: dp[j][k+1] = dp[j][k] else: dp[j][k+1] = [dp[j][k][0], dp[j][k][1][:]] # If we take the line if j > 0: sub, how = dp[j-1][0] sub += graph[i-1] + (k-8)**2 if sub < dp[j][0][0]: dp[j][0] = [sub, how + [i]] # Find the minimum cost and its corresponding path min_cost, path = min((dp[lines_left][k][0], dp[lines_left][k][1]) for k in range(11)) return min_cost, path 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>
assert answer == expected, f'Wrong answer; got {answer} instead of {expected}'
^^^^^^^^^^^^^^^^^^
AssertionError: Wrong answer; got (1000000000.0, []) instead of (165, [3, 11, 16, 24, 30, 40, 49, 57, 64, 75, 86, 94])
Testing if the previous output contains the string All tests passed
: False
Resulting in output: True