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.
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.
solution：
bool hasPathSum(TreeNode* root, int sum) { if (root == NULL) return false; else if (root->val == sum && root->left == NULL && root->right == NULL) return true; else return (hasPathSum(root->left, sum - root->val) || hasPathSum(root->right, sum - root->val)); }
原文：http://www.cnblogs.com/gattaca/p/4671990.html