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
**Recursive Function:** The `solve_dp` function takes three arguments: a list `graph` representing the distances between consecutive lines, an integer `lines_left` representing the number of lines left to take, and an integer `distance_since_last` representing the distance since the last line was taken. It returns a tuple containing two values: 1. The minimum cost of taking a sequence of lines while meeting the given constraints. 2. A list of the indices of the lines taken in order. The function uses dynamic programming with memoization to efficiently find the optimal solution. It considers two options: - **Option 1 (Skip Line):** If there are still lines left and the distance since the last line is less than 10, the function recursively calls itself with the next line in the graph, the same number of lines left, and the increased distance. - **Option 2 (Take Line):** If there are lines left, the function recursively calls itself with the next line in the graph, the reduced number of lines left, and the reset distance. It adds the distance of the current line and a penalty based on the square of the difference between the current distance and 8 to the cost. The function returns the minimum cost and the corresponding sequence of lines taken. **Iterative Function:** The iterative version of the function, `solve_iterative`, has the same type signature as the recursive function and returns the same output. However, it uses an iterative approach with dynamic programming to achieve the same result without recursion. Here's the code for 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 | def solve_iterative(graph, lines_left, distance_since_last): # Initialize a 3D table to store the minimum cost and sequence for each state dp = [[[1e9, []] for _ in range(11)] for _ in range(lines_left + 1)] # Base case: no lines left or no more lines to take dp[0][0][0] = (0, []) # Iterate over the number of lines left for lines in range(1, lines_left + 1): # Iterate over the distance since the last line for dist in range(10): # Iterate over the graph for i in range(len(graph)): # Option 1: skip the line if dist < 10: dp[lines][dist][i] = min(dp[lines][dist][i], dp[lines][dist + 1][i + 1]) # Option 2: take the line if lines > 0: sub, how = dp[lines - 1][0][i + 1] sub += graph[i] + (dist - 8) ** 2 dp[lines][dist][i] = min(dp[lines][dist][i], (sub, how + [i + 1])) # Return the minimum cost and sequence for the given state return dp[lines_left][distance_since_last][0] |
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 | def solve_iterative(graph, lines_left, distance_since_last): # Initialize a 3D table to store the minimum cost and sequence for each state dp = [[[1e9, []] for _ in range(11)] for _ in range(lines_left + 1)] # Base case: no lines left or no more lines to take dp[0][0][0] = (0, []) # Iterate over the number of lines left for lines in range(1, lines_left + 1): # Iterate over the distance since the last line for dist in range(10): # Iterate over the graph for i in range(len(graph)): # Option 1: skip the line if dist < 10: dp[lines][dist][i] = min(dp[lines][dist][i], dp[lines][dist + 1][i + 1]) # Option 2: take the line if lines > 0: sub, how = dp[lines - 1][0][i + 1] sub += graph[i] + (dist - 8) ** 2 dp[lines][dist][i] = min(dp[lines][dist][i], (sub, how + [i + 1])) # Return the minimum cost and sequence for the given state return dp[lines_left][distance_since_last][0] |
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 | def solve_iterative(graph, lines_left, distance_since_last): # Initialize a 3D table to store the minimum cost and sequence for each state dp = [[[1e9, []] for _ in range(11)] for _ in range(lines_left + 1)] # Base case: no lines left or no more lines to take dp[0][0][0] = (0, []) # Iterate over the number of lines left for lines in range(1, lines_left + 1): # Iterate over the distance since the last line for dist in range(10): # Iterate over the graph for i in range(len(graph)): # Option 1: skip the line if dist < 10: dp[lines][dist][i] = min(dp[lines][dist][i], dp[lines][dist + 1][i + 1]) # Option 2: take the line if lines > 0: sub, how = dp[lines - 1][0][i + 1] sub += graph[i] + (dist - 8) ** 2 dp[lines][dist][i] = min(dp[lines][dist][i], (sub, how + [i + 1])) # Return the minimum cost and sequence for the given state return dp[lines_left][distance_since_last][0] 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 57, in <module>
answer = solve_iterative(tuple(mylist), len(mylist)//8, 4)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/src/app/main.py", line 17, in solve_iterative
dp[lines][dist][i] = min(dp[lines][dist][i], dp[lines][dist + 1][i + 1])
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: '<' not supported between instances of 'list' and 'float'
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 function `solve_dp` tries to find the best way to go from the first line to the last one in a graph of lines, where each line has a certain length. The function takes three parameters: the graph of lines, the number of lines left to go, and the distance since the last line was taken. The function returns a tuple with two elements: the minimum distance to go from the first line to the last one, and the list of lines that were taken. The function first checks if the number of lines left to go is greater than the number of lines in the graph. If this is the case, then it returns a large number (1e9) to indicate that there is no valid solution. If the number of lines left to go is 0 and the number of lines in the graph is also 0, then it returns 0 to indicate that the solution is valid and the list of lines that were taken is empty. The function then considers two options: 1. Don't take the first line. In this case, the function calls itself recursively with the graph of lines without the first line, the same number of lines left to go, and the distance since the last line was taken plus 1. 2. Take the first line. In this case, the function calls itself recursively with the graph of lines without the first line, the number of lines left to go minus 1, and the distance since the last line was taken reset to 0. The function then returns the minimum of the two options. **Iterative Solution** The iterative solution is as follows:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | def solve_iterative(graph, lines_left, distance_since_last): # Initialize the dp table dp = [[(1e9, []) for _ in range(lines_left+1)] for _ in range(len(graph)+1)] dp[len(graph)][0] = (0, []) # Iterate over the graph and the number of lines left for i in range(len(graph)-1,-1,-1): for j in range(lines_left+1): # Option 1: don't take the line if distance_since_last < 10: dp[i][j] = min(dp[i][j], dp[i+1][j]) # Option 2: take the line if j > 0: sub, how = dp[i+1][j-1] sub += graph[i] + (distance_since_last-8)**2 dp[i][j] = min(dp[i][j], (sub, how + [len(graph)-i])) return dp[0][lines_left] |
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 | def solve_iterative(graph, lines_left, distance_since_last): # Initialize the dp table dp = [[(1e9, []) for _ in range(lines_left+1)] for _ in range(len(graph)+1)] dp[len(graph)][0] = (0, []) # Iterate over the graph and the number of lines left for i in range(len(graph)-1,-1,-1): for j in range(lines_left+1): # Option 1: don't take the line if distance_since_last < 10: dp[i][j] = min(dp[i][j], dp[i+1][j]) # Option 2: take the line if j > 0: sub, how = dp[i+1][j-1] sub += graph[i] + (distance_since_last-8)**2 dp[i][j] = min(dp[i][j], (sub, how + [len(graph)-i])) return dp[0][lines_left] |
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 | def solve_iterative(graph, lines_left, distance_since_last): # Initialize the dp table dp = [[(1e9, []) for _ in range(lines_left+1)] for _ in range(len(graph)+1)] dp[len(graph)][0] = (0, []) # Iterate over the graph and the number of lines left for i in range(len(graph)-1,-1,-1): for j in range(lines_left+1): # Option 1: don't take the line if distance_since_last < 10: dp[i][j] = min(dp[i][j], dp[i+1][j]) # Option 2: take the line if j > 0: sub, how = dp[i+1][j-1] sub += graph[i] + (distance_since_last-8)**2 dp[i][j] = min(dp[i][j], (sub, how + [len(graph)-i])) return dp[0][lines_left] 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>
assert answer == expected, f'Wrong answer; got {answer} instead of {expected}'
^^^^^^^^^^^^^^^^^^
AssertionError: Wrong answer; got (258, [2, 3, 23, 35, 39, 40, 42, 54, 58, 70, 80, 100]) instead of (189, [2, 13, 23, 30, 39, 45, 54, 63, 70, 80, 87, 95])
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 code provided is a dynamic programming solution to a problem where we have a list of lines of different lengths and we want to find the shortest path to draw all the lines without overlapping. The function `solve_dp` takes three arguments: the list of lines, the number of lines left to draw, and the distance since the last line was drawn. It returns a tuple with the minimum distance to draw all the lines and the list of lines that were drawn. The function uses a recursive approach, where it tries two options: - Don't take the line: in this case, the distance is not updated and the number of lines left is decremented by one. - Take the line: in this case, the distance is updated by adding the length of the line plus the square of the distance since the last line was drawn, and the number of lines left is decremented by one. The function uses memoization to avoid recomputing the same subproblems multiple times. The iterative version of the function is as follows:
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 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) dp = [[[1e9 for _ in range(11)] for _ in range(lines_left+1)] for _ in range(n+1)] dp[n][0][0] = 0 for i in range(n-1,-1,-1): for j in range(lines_left+1): for k in range(11): # option 1: don't take the line if k < 10: dp[i][j][k] = min(dp[i][j][k], dp[i+1][j][k+1]) # option 2: take the line if j > 0: dp[i][j][0] = min(dp[i][j][0], dp[i+1][j-1][0] + graph[i] + (k-8)**2) dp[i][j][k] = min(dp[i][j][k], dp[i+1][j-1][k] + graph[i] + (k-8)**2) distance = dp[0][lines_left][0] path = [] i = 0 j = lines_left k = 0 while i != n: if dp[i][j][k] == dp[i+1][j][k+1]: k += 1 else: path.append(len(graph) - i) j -= 1 i += 1 return distance, 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 27 28 29 30 31 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) dp = [[[1e9 for _ in range(11)] for _ in range(lines_left+1)] for _ in range(n+1)] dp[n][0][0] = 0 for i in range(n-1,-1,-1): for j in range(lines_left+1): for k in range(11): # option 1: don't take the line if k < 10: dp[i][j][k] = min(dp[i][j][k], dp[i+1][j][k+1]) # option 2: take the line if j > 0: dp[i][j][0] = min(dp[i][j][0], dp[i+1][j-1][0] + graph[i] + (k-8)**2) dp[i][j][k] = min(dp[i][j][k], dp[i+1][j-1][k] + graph[i] + (k-8)**2) distance = dp[0][lines_left][0] path = [] i = 0 j = lines_left k = 0 while i != n: if dp[i][j][k] == dp[i+1][j][k+1]: k += 1 else: path.append(len(graph) - i) j -= 1 i += 1 return distance, 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 61 62 63 64 65 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) dp = [[[1e9 for _ in range(11)] for _ in range(lines_left+1)] for _ in range(n+1)] dp[n][0][0] = 0 for i in range(n-1,-1,-1): for j in range(lines_left+1): for k in range(11): # option 1: don't take the line if k < 10: dp[i][j][k] = min(dp[i][j][k], dp[i+1][j][k+1]) # option 2: take the line if j > 0: dp[i][j][0] = min(dp[i][j][0], dp[i+1][j-1][0] + graph[i] + (k-8)**2) dp[i][j][k] = min(dp[i][j][k], dp[i+1][j-1][k] + graph[i] + (k-8)**2) distance = dp[0][lines_left][0] path = [] i = 0 j = lines_left k = 0 while i != n: if dp[i][j][k] == dp[i+1][j][k+1]: k += 1 else: path.append(len(graph) - i) j -= 1 i += 1 return distance, 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 63, in <module>
answer = solve_iterative(tuple(mylist), len(mylist)//8, 4)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/src/app/main.py", line 25, in solve_iterative
if dp[i][j][k] == dp[i+1][j][k+1]:
~~~~~~~~~~^^^^^
IndexError: list index out of range
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
This function takes three inputs: - A list of integers `graph` representing the height of the lines. - An integer `lines_left` representing the number of lines remaining to take. - An integer `distance_since_last` representing the distance since the last line was taken. The function returns a tuple of two elements: - A number representing the minimum total cost of taking the lines. - A list of integers representing the indices of the lines that were taken. The function uses dynamic programming to solve the problem. It stores the minimum cost of taking the lines in a dictionary, so that it does not have to recompute the same subproblems multiple times. The function has two base cases: - If the number of lines remaining is less than the number of lines in the graph, then the function returns a large number to indicate that it is not possible to take all of the lines. - If the number of lines remaining is 0 and the number of lines in the graph is 0, then the function returns 0 to indicate that it is possible to take all of the lines without taking any penalty. The function has two options for each line: - It can choose not to take the line. In this case, the cost is the cost of taking the remaining lines, and the number of lines remaining is decreased by 1. - It can choose to take the line. In this case, the cost is the cost of taking the remaining lines, plus the height of the line, plus the square of the distance since the last line was taken. The number of lines remaining is decreased by 1, and the distance since the last line was taken is reset to 0. The function returns the minimum cost of the two options. The following code converts the recursive function to an iterative one:
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): # Initialize the dp table dp = {} dp[(len(graph), lines_left, distance_since_last)] = (0, []) # Iterate over the graph for i in range(len(graph)-1, -1, -1): for j in range(lines_left+1): for k in range(distance_since_last+1): # Option 1: don't take the line if k < 10: dp[(i, j, k)] = min(dp[(i, j, k)], dp[(i+1, j, k+1)]) # Option 2: take the line if j > 0: sub, how = dp[(i+1, j-1, 0)] sub += graph[i] + (k-8)**2 dp[(i, j, k)] = min(dp[(i, j, k)], (sub, how + [len(graph)-i])) # Return the minimum cost 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 | def solve_iterative(graph, lines_left, distance_since_last): # Initialize the dp table dp = {} dp[(len(graph), lines_left, distance_since_last)] = (0, []) # Iterate over the graph for i in range(len(graph)-1, -1, -1): for j in range(lines_left+1): for k in range(distance_since_last+1): # Option 1: don't take the line if k < 10: dp[(i, j, k)] = min(dp[(i, j, k)], dp[(i+1, j, k+1)]) # Option 2: take the line if j > 0: sub, how = dp[(i+1, j-1, 0)] sub += graph[i] + (k-8)**2 dp[(i, j, k)] = min(dp[(i, j, k)], (sub, how + [len(graph)-i])) # Return the minimum cost 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 | def solve_iterative(graph, lines_left, distance_since_last): # Initialize the dp table dp = {} dp[(len(graph), lines_left, distance_since_last)] = (0, []) # Iterate over the graph for i in range(len(graph)-1, -1, -1): for j in range(lines_left+1): for k in range(distance_since_last+1): # Option 1: don't take the line if k < 10: dp[(i, j, k)] = min(dp[(i, j, k)], dp[(i+1, j, k+1)]) # Option 2: take the line if j > 0: sub, how = dp[(i+1, j-1, 0)] sub += graph[i] + (k-8)**2 dp[(i, j, k)] = min(dp[(i, j, k)], (sub, how + [len(graph)-i])) # Return the minimum cost 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 53, in <module>
answer = solve_iterative(tuple(mylist), len(mylist)//8, 4)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/src/app/main.py", line 13, in solve_iterative
dp[(i, j, k)] = min(dp[(i, j, k)], dp[(i+1, j, k+1)])
~~^^^^^^^^^^^
KeyError: (99, 0, 0)
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 function `solve_dp` takes a graph, the number of lines left to read, and the distance since the last line read. It returns the minimum distance to read all the lines in the graph and the order in which they should be read. The function is recursive and uses memoization to avoid recomputing the same subproblems. The memoization is done using the `@lru_cache` decorator. The function has a cubic complexity because it has to consider all possible combinations of lines to read. The following code is an iterative version of the function:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) dp = [[[1e9, []] for _ in range(lines_left+1)] for _ in range(distance_since_last+1)] dp[0][0][0] = (0, []) for i in range(distance_since_last+1): for j in range(lines_left+1): # option 1: don't take the line if j > 0: dp[i][j][0] = min(dp[i][j][0], dp[i][j-1][0]) # option 2: take the line if i > 0: dp[i][j][0] = min(dp[i][j][0], dp[i-1][j][0] + graph[i-1] + (i-9)**2) dp[i][j][1] = [i] + dp[i-1][j][1] return dp[distance_since_last][lines_left] |
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 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) dp = [[[1e9, []] for _ in range(lines_left+1)] for _ in range(distance_since_last+1)] dp[0][0][0] = (0, []) for i in range(distance_since_last+1): for j in range(lines_left+1): # option 1: don't take the line if j > 0: dp[i][j][0] = min(dp[i][j][0], dp[i][j-1][0]) # option 2: take the line if i > 0: dp[i][j][0] = min(dp[i][j][0], dp[i-1][j][0] + graph[i-1] + (i-9)**2) dp[i][j][1] = [i] + dp[i-1][j][1] return dp[distance_since_last][lines_left] |
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 | def solve_iterative(graph, lines_left, distance_since_last): n = len(graph) dp = [[[1e9, []] for _ in range(lines_left+1)] for _ in range(distance_since_last+1)] dp[0][0][0] = (0, []) for i in range(distance_since_last+1): for j in range(lines_left+1): # option 1: don't take the line if j > 0: dp[i][j][0] = min(dp[i][j][0], dp[i][j-1][0]) # option 2: take the line if i > 0: dp[i][j][0] = min(dp[i][j][0], dp[i-1][j][0] + graph[i-1] + (i-9)**2) dp[i][j][1] = [i] + dp[i-1][j][1] return dp[distance_since_last][lines_left] 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 49, in <module>
answer = solve_iterative(tuple(mylist), len(mylist)//8, 4)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/src/app/main.py", line 11, in solve_iterative
dp[i][j][0] = min(dp[i][j][0], dp[i][j-1][0])
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: '<' not supported between instances of 'tuple' and 'float'
Testing if the previous output contains the string All tests passed
: False
Resulting in output: True