题目：
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: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.
链接：http://leetcode.com/problems/path-sum/
一刷，DFS
class Solution(object): def hasPathSum(self, root, sum): if not root: return False if not root.left and not root.right and sum == root.val: return True return self.hasPathSum(root.left, sum - root.val) or self.hasPathSum(root.right, sum - root.val)
原文：http://www.cnblogs.com/panini/p/5609870.html