[LeetCode] Path Sum

 1 /**
 2  * Definition for binary tree
 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         int tmpSum=0;
13         Stack<TreeNode> nodeStack = new Stack<TreeNode>();
14         TreeNode nowNode = root;
15         boolean popNode = false;
16         
17         if (root==null) return false;
18         if (root.val==sum && root.left==null && root.right==null) return true;
19         
20         while (!(nowNode==root && popNode)) {
21             if (!popNode) {
22                 if (nowNode == null) {
23                     popNode = true;
24                 } else {
25                     tmpSum += nowNode.val;
26                     nodeStack.push(nowNode);
27                     nowNode = nowNode.left;
28                 }
29             } else {
30                 if (nowNode == nodeStack.peek().right) {
31                     if (nowNode==null && tmpSum==sum && nodeStack.peek().left==null) return true;
32                     nowNode = nodeStack.pop();
33                     tmpSum -= nowNode.val;
34                 } else {
35                     nowNode = nodeStack.peek().right;
36                     popNode = false;
37                 }
38             }
39         }
40         return false;
41     }
42 }