[LeetCode]题解（python）：112 Path Sum

题目来源

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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.

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题意分析

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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

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题目思路

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递归遍历，通过一个不断递减的sum值去判断。

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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)