Path Sum

看了一下数据结构中树的操作，A这题感觉好一点了。Symmetric Tree和这个很相似来着，可以借鉴一下这个思路。用递归处理

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.

 1 /**
 2  * Definition for binary tree
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *  
 7  *     TreeNode right;
 8  *     TreeNode(int x) { val = x; }
 9  * }
10  */
11 public class Solution {
12     boolean flag = false;
13     
14     public boolean hasPathSum(TreeNode root, int sum) {
15         if(null == root)
16             return false;
17         hasPathSum1(root, sum);
18         return flag;
19     }
20     public boolean hasPathSum1(TreeNode root, int sum) {
21         if(null == root.left && null == root.right){
22             if(sum == root.val)
23                 flag = true;
24             return sum == root.val;
25         }
26             
27         else 
28             return hasPathSum(root.left, sum - root.val) ||
29         
30              hasPathSum(root.right, sum - root.val);
31     }
32 }

 PS:这样也是可以的

 1 /**
 2  * Definition for binary tree
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *  
 7  *     TreeNode right;
 8  *     TreeNode(int x) { val = x; }
 9  * }
10  */
11 public class Solution {
12     public boolean hasPathSum(TreeNode root, int sum) {
13         if(null == root)
14             return false;
15         if(null == root.left && null == root.right){
16             
17             return sum == root.val;
18         }
19             
20         else 
21             return hasPathSum(root.left, sum - root.val) ||
22         
23              hasPathSum(root.right, sum - root.val);
24     }
25 }

 

posted on 2014-11-03 22:23  luckygxf  阅读(160)  评论(0)  编辑  收藏  举报

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