Path Sum

题目

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.

方法

本质是树的遍历，使用树的先序遍历，并使用一个变量tempSum来记录遍历到当前结点的和。

public boolean preOrder(TreeNode node, int sum, int tempSum) {if (node != null) {tempSum += node.val;if (node.left == null && node.right == null) {if (tempSum == sum) {return true;} else {return false;}}return preOrder(node.left, sum, tempSum) || preOrder(node.right, sum, tempSum);} return false;}    public boolean hasPathSum(TreeNode root, int sum) {     return preOrder(root, sum, 0);    }