[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）

 1 # Definition for a binary tree node.
 2 # class TreeNode(object):
 3 #     def __init__(self, x):
 4 #         self.val = x
 5 #         self.left = None
 6 #         self.right = None
 7 
 8 class Solution(object):
 9     def hasPathSum(self, root, sum):
10         """
11         :type root: TreeNode
12         :type sum: int
13         :rtype: bool
14         """
15         if root == None:
16             return False
17         if root.left == None and root.right == None:
18             return root.val == sum
19         return self.hasPathSum(root.left, sum - root.val) or self.hasPathSum(root.right, sum - root.val)
20