int BinaryTreeLevelKSize(BTNode* root, int k)
{assert(k > 0);if (root == NULL){return 0;}if (k == 1){return 1;}return BinaryTreeLevelKSize(root->left, k - 1) + BinaryTreeLevelKSize(root->right, k - 1);
}
int BinaryTreeLevelKSize(BTNode* root, int k)
{assert(k > 0);if (root == NULL){return 0;}if (k == 1){return 1;}return BinaryTreeLevelKSize(root->left, k - 1) + BinaryTreeLevelKSize(root->right, k - 1);
}