Path_Sum.cpp

// Source : https://leetcode-cn.com/problems/path-sum/description/
// Number : 112
// Author : HL
// Date   : 2018-09-25
// Kill   : 97.16%

/********************************************************************************** 
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.
**********************************************************************************/

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool hasPathSum(TreeNode* root, int sum) {
        if (root == NULL)
            return false;
        if (root->val == sum && 
            root->left == NULL && 
            root->right == NULL)
            return true;
        
        return hasPathSum(root->left, sum - root->val) || 
               hasPathSum(root->right, sum - root->val);
    }
};