题目描写叙述：

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.

              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.

bool Solution::hasPathSum(TreeNode *root, int sum)
{
    if(root == NULL)
        return false;
    if(root->left == NULL && root->right == NULL)
        return root->val - sum;
    else
        return hasPathSum(root->left,sum-root->val) || hasPathSum(root->right,sum-root->val);
}