[LeetCode]题解（python）：112 Path Sum

题目来源

---

https://leetcode.com/problems/path-sum/

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

---

题意分析

---

Input: a binary tree, sum

Output: True or False

Conditions:判断是否存在一条路径，从root-leaf的路径，使得路径的value的和等于sum

---

题目思路

---

递归遍历，通过一个不断递减的sum值去判断。

---

AC代码（Python）

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

class Solution(object):
    def hasPathSum(self, root, sum):
        """
        :type root: TreeNode
        :type sum: int
        :rtype: bool
        """
        if root == None:
            return False
        if root.left == None and root.right == None:
            return root.val == sum
        return self.hasPathSum(root.left, sum - root.val) or self.hasPathSum(root.right, sum - root.val)