Path Sum II(Leetcode113)

Question

class Solution:
    def searchPath(self,node,targetSum,path,result):
        if (not node.left) and (not node.right) and (targetSum==0):
            result.append(path)
        if (not node.left) and (not node.right) and (targetSum!=0):
            return 
        if node.left:
            path.append(node.left.val)
            self.searchPath(node.left,targetSum-node.left.val,path,result)
            path.pop()
        if node.right:
            path.append(node.right.val)
            self.searchPath(node.right,targetSum-node.right.val,path,result)
            path.pop()

        return result

The answer will be wrong. But if I change result.append(path) to result.append(path[:]) The answer will be correct. What's the difference?

luk2302 · Accepted Answer · 2021-11-02 13:42:04Z

1

The difference is that path[:] creates a shallow copy of path. Later mutating path in the following ifs does no longer change the path copy that was appended to result.

Appending path directly and later appending something to path changes the path that is already appended to result, effectively changing what result contains.

answered Nov 2, 2021 at 13:42

luk2302

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