113. Path Sum II.md

113. Path Sum II

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.

Note: A leaf is a node with no children.

Example:

Given the below binary tree and sum = 22,

      5
     / \
    4   8
   /   / \
  11  13  4
 /  \    / \
7    2  5   1
Return:

[
   [5,4,11,2],
   [5,8,4,5]
]

Idea

There is one thing need to notice, at line 23, we divided it into 2 sub-tree, so in case left currPath influence right currPath, I make a hard copy of it.

Solution

class Solution:
    def pathSum(self, root: TreeNode, sum: int) -> List[List[int]]:
        self.ans = []
        self.totalSum = sum
        self.pathSumHelper(root, 0, [])
        return self.ans

    def pathSumHelper(self, node, currSum, currPath):
        if not node:
            return False
        currSum += node.val
        currPath.append(node.val)
        if not node.left and not node.right and currSum == self.totalSum:
            self.ans.append(currPath)
        else:
            self.pathSumHelper(node.left, currSum, currPath[:]) # to avoid influence right path
            self.pathSumHelper(node.right, currSum, currPath)