LeetCode 112 Path Sum

標籤：java   leetcode   

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.

思路：使用先序遍曆，不過本人在壓棧的時候改變了節點的值。

/** * Definition for binary tree * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {public boolean hasPathSum(TreeNode root, int sum) {    if(root == null ) return false;Stack<TreeNode> s = new Stack<TreeNode>();s.push(root);while (!s.isEmpty()) {TreeNode temp = s.peek();s.pop();if (temp.right != null) {temp.right.val += temp.val;s.push(temp.right);}if (temp.left != null) {temp.left.val += temp.val;s.push(temp.left);}if (temp.left == null && temp.right == null && temp.val == sum)return true;}return false;}}

LeetCode 112 Path Sum