leetcode--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.

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.

分类：二叉树

题意：在二叉树中查找和为sum的路径(从根节点到叶子节点)

解法1：递归。由于sum可能是负数，所以必须遍历到根节点，过程中不能剪枝。

[java] view plain copy

1. /** 
2.  * Definition for a binary tree node. 
3.  * public class TreeNode { 
4.  *     int val; 
5.  *     TreeNode left; 
6.  *     TreeNode right; 
7.  *     TreeNode(int x) { val = x; } 
8.  * } 
9.  */  
10. public class Solution {  
11.     public boolean hasPathSum(TreeNode root, int sum) {  
12.         if(root==null) return false;  
13.         if(root.val==sum &&root.left==null&&root.right==null){  
14.             return true;  
15.         }else{  
16.             return hasPathSum(root.left, sum-root.val)||hasPathSum(root.right, sum-root.val);  
17.         }  
18.     }  
19. } 

原文链接http://blog.csdn.net/crazy__chen/article/details/46379151