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.

              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 binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
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) {
		return dfs(root,sum,0);
    }
private:
	bool dfs(TreeNode *root,int sum,int n)
	{
		if(root == NULL) return false;
		n += root->val;
		if(root->left == NULL && root->right == NULL) return n == sum;
		return dfs(root->left,sum,n) || dfs(root->right,sum,n);
	}
};

leetcode - Path Sum