在Python的遞歸函數中將值存儲到列表的問題

Question

我正在嘗試編寫一個Python函數，該函數存儲網格上兩點之間的所有路徑。 這是原始問題，我從答案中得到啟發，並嘗試在Python中創建類似版本。

我能夠通過應用遞歸函數成功打印出所有找到的路徑，但是問題是當我需要將它們存儲在列表中時，我得到了一個空列表。 我嘗試使用全局變量和局部變量作為存儲列表，它們給出了相同的結果。 有人可以在下面的代碼中發表評論，並建議我做錯了什么嗎？

非常感謝！

import numpy as np

#initialize a matrix
grid = np.arange(0, 1225).reshape((35,35))
m = 10
n = 5
#starting point
s = (0, 0)
#target point
d = (n, m)
results = []

#a function to find the next step in the path
def next_step(x, y):
    step = []
    dx = [0, 1]
    dy = [1, 0]

    for i in range(2):
        next_x = x + dx[i]
        next_y = y + dy[i]
        if next_x >= 0 and next_x <= n and next_y >= 0 and next_y <= m:
            step.append((next_x, next_y))
    return step

def print_all_path(s, d, visited, path):
    global results
    visited[s[0]][s[1]] = True
    path.append(grid[s[0]][s[1]])

    if s == d:
        results.append(path)
        print(path)
    else:
        for step in next_step(s[0], s[1]):
            if visited[step[0],step[1]] == False:
                print_all_path(step, d, visited, path)
    path.pop()
    visited[s[0]][s[1]] = False

def print_path(s, d):
    visited = np.zeros((35,35), dtype = bool)
    path = []
    print_all_path(s, d, visited, path)

print_path(s, d)

Answer 1

問題可能是當您追加時，您只追加了path我懷疑您做了這樣的事情：

# global 
all_lists = []

# your functions
...
def print_all_path(s, d, visited, path):
    global results
    visited[s[0]][s[1]] = True
    path.append(grid[s[0]][s[1]])

    if s == d:
        results.append(path)
        print(path)
        all_lists.append(path)
...

但是，路徑仍鏈接到原始path變量。

您可以使用以下方法解決此問題：

all_lists.append(path + [])

這將復制列表並刪除鏈接

所以整個程序現在

import numpy as np

#initialize a matrix
grid = np.arange(0, 1225).reshape((35,35))
m = 10
n = 5
#starting point
s = (0, 0)
#target point
d = (n, m)
results = []
all_paths = []

#a function to find the next step in the path
def next_step(x, y):
    step = []
    dx = [0, 1]
    dy = [1, 0]

    for i in range(2):
        next_x = x + dx[i]
        next_y = y + dy[i]
        if next_x >= 0 and next_x <= n and next_y >= 0 and next_y <= m:
            step.append((next_x, next_y))
    return step

def print_all_path(s, d, visited, path):
    global results
    visited[s[0]][s[1]] = True
    path.append(grid[s[0]][s[1]])

    if s == d:
        results.append(path)
        all_paths.append(path + [])
        #print(path)
    else:
        for step in next_step(s[0], s[1]):
            if visited[step[0],step[1]] == False:
                print_all_path(step, d, visited, path)
    path.pop()
    visited[s[0]][s[1]] = False

def print_path(s, d):
    visited = np.zeros((35,35), dtype = bool)
    path = []
    print_all_path(s, d, visited, path)


print_path(s, d)
print all_paths