[Leetcode]112. Path Sum -David_Lin

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


思路：递归所有路径，如果到达叶子节点，并且此时sum=0，则返回true;

 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 class Solution {
11     public boolean hasPathSum(TreeNode root, int sum) {
12         if (root==null)
13             return flase;            //一开始如果传进来空引用，则返回false;
14         sum-=root.val;
15         if (root.left==null&&&root.right==null){    //如果已经到了叶子
16             if (sum==0)                                        //如果此时sum=0，则返回true
17                 return true;                                     //否则返回false
18             else 
19                 return false;
20         }
21         //同时递归左右子树
22         return hasPathSum(root.left,sum)||hasPathSum(root.right,sum);
23     }
24 }

 

posted @ 2017-10-19 06:59  SkyMelody  阅读(84)  评论(0)  编辑  收藏  举报