递归中的列表更新错误[网格中的机器人]Python

Question

def path_through_grid(grid):
  path = ["start"]
  helper(grid, 0, 0, path)
  print("final", path)
  if path[-1]=='end':
    return path
  else:
    return None

def helper(grid, r, c, path):
  print("start---", r, " - ", c, "path: ", path)
  if r == len(grid) or c == len(grid[0]):
    return
  if grid[r][c] == 1:
    return
  if r == len(grid)-1 and c == len(grid[0])-1:
    print("inside")
    path.append("end")
    return
  path.append("right")
  helper(grid, r, c+1, path)
  print("middle---", r, " - ", c, "path: ", path)
  if path[-1]=="end":
    print("inside 2", path)
    return
  path = path[:-1]
  print("after", path)
  path.append("down")
  helper(grid, r+1, c, path)
  print("end---", r, " - ", c, "path: ", path)

import unittest

class Test(unittest.TestCase):
  def test_path_through_grid(self):
    grid = [[0,1],
            [0,0]]
    self.assertEqual(path_through_grid(grid), ["start", "down", "right", "end"])

if __name__ == "__main__":
  unittest.main()

Answer 1

问题出在这一行：

path = path[:-1]

这里指定给path，这是一个错误。您应该只变异路径，而不是分配给它。分配时，调用方的路径将不再受影响--您现在已经创建了一个不同的列表引用。

因此，请使用减小路径大小的方法

path.pop()