死 Kernel 在 Jupyter Notebook 中运行代码，Python 3

Question

I'm currently writing a short code as follows that returns the co-ordinates and size of the longest path in a grid with the following constraints:

1. Only move up,down,left,right
2. Only move to a cell that has a maximum difference of 1
3. Cannot pass through a cell twice
4. Must start in the top row

My code is as follows:

import numpy as np
grid = np.random.randint(3, size=(5, 5))

def get_longest_path(grid):

    # setup
    cols, rows = grid.shape # length, width

    # pathfinder function
    def pathfinder(i,j):        
        best, best_path = 0, []
        udlr = {(i - 1, j), (i + 1, j), (i, j - 1), (i, j + 1)}  # up down left right directions
        for x, y in udlr:
            if 0 <= x < cols and 0 <= y < rows and abs(grid[x][y] - grid[i][j]) <= 1: # check it's in bounds   
                #grid[x][y] > grid[i][j]
                n, path = pathfinder(x,y)
                if n > best:
                    best, best_path = n, path
        return best + 1, [(i,j)] + best_path
        
    
    #return longest path
    return max(pathfinder(0,j) for j in range(rows))

get_longest_path(grid)

As far as I can tell, it works fine if I use the constraint grid[x][y] > grid[i][j] in place of abs(grid[x][y] - grid[i][j]) <= 1 . However, if I run this as it is, the Jupyter kernel dies straight away.

Perhaps it starts an infinite loop, but I can't see why this would be the case.

Any advice would be appreciated, thank you.

Answer 1

try defining pathfinder() outside and above get_longest_path()