leetcode -- 112. Path Sum

题目描述

题目难度：Easy
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.

Note: A leaf is a node with no children.

AC代码

要注意判断条件：
只有当前节点是叶子节点且根节点到叶子节点和为sum才返回true。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    private boolean hasPathSum = false;
    public boolean hasPathSum(TreeNode root, int sum) {
        if(root == null) return hasPathSum;
        hasPathSum(root, sum, 0);
        return hasPathSum;
    }
    
    private void hasPathSum(TreeNode root, int sum, int cur){
        if(root == null) return;
        if(root.left == null && root.right == null) {
            if(cur + root.val == sum){
                hasPathSum = true;
                return;
            }
        }
        hasPathSum(root.left, sum, cur + root.val);
        hasPathSum(root.right, sum, cur + root.val);
    }
}