[LeetCode] 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.

递归，DFS，用stack实现还没想好怎么弄。。

/**
 * Definition for binary tree
 * 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->left == NULL && root->right == NULL)
        {
            if(root->val == sum)
                return true;
            else
                return false;
        }
        bool left = false;
        bool right= false;

        if(root->left)
            left = hasPathSum(root->left, sum - root->val);
        if(root->right)
            right = hasPathSum(root->right, sum - root->val);

        return (left || right);
    }
};