原题地址:https://oj.leetcode.com/problems/path-sum/

题意:

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.

For example:
Given the below binary tree and sum = 22,

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

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

解题思路:使用递归解决。

代码:

# Definition for a  binary tree node
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None class Solution:
# @param root, a tree node
# @param sum, an integer
# @return a boolean
def hasPathSum(self, root, sum):
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)

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