LeetCode_Path Sum II

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.
（二叉树路径和并返回相应路径）

Example:

1. 递归

这道题是很清晰的递归的问题，需要注意的是节点的值可能是负值。具体实现方法如下：

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def pathSum(self, root: TreeNode, sum: int) -> List[List[int]]:
        def path_helper(head, path, sum):
            if sum == head.val and not head.left and not head.right:
                self.paths.append(path+[head.val])
                return
            
            if head.left:
                path_helper(head.left, path+[head.val], sum-head.val)
            if head.right:
                path_helper(head.right, path+[head.val], sum-head.val)
                  
        if not root:
            return []
        
        self.paths = []
        path_helper(root, [], sum)
        
        return self.paths