题目链接：112. Path Sum

题目描述

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.

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.

解题思路

递归求解：

如果为叶子结点且值的和为目标 则返回ture，否则 递归左右子树，其中之一返回ture即可。

题解

    public boolean hasPathSum(TreeNode root, int sum) {
        if(root == null) return false;
        if(root.left==null && root.right==null && sum== root.val) return true;
        int temp = sum-root.val;
        
        return hasPathSum(root.left,temp) || hasPathSum(root.right,temp);
    }