[LeetCode][JavaScript]Path Sum

Path Sum

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.

https://leetcode.com/problems/path-sum/ 

---

判断是否有一条从根到叶子的路径的和为sum。

如果不是叶子节点，递归进去，如果是叶子节点，计算路径是不是等于sum。

两道类似的题：

Binary Tree Paths : http://www.cnblogs.com/Liok3187/p/4735368.html

Path Sum II : http://www.cnblogs.com/Liok3187/p/4869538.html

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @param {number} sum
 * @return {boolean}
 */
var hasPathSum = function(root, sum) {
    if(root && root.val !== undefined){
        return hasSum(root, 0);
    }
    return false;

    function hasSum(node, value){
        var isLeaf = true, tmp;
        if(node.left){
            isLeaf = false;
            tmp = hasSum(node.left, value + node.val);
            if(tmp === true){
                return true;
            }
        }
        if(node.right){
            isLeaf = false;
            tmp = hasSum(node.right, value + node.val);
            if(tmp === true){
                return true;
            }
        }
        if(isLeaf){
            tmp = value + node.val;
            if(tmp === sum){
                return true;
            }
        }
        return false;
    }
};