二分搜索树

template<typename Key,typename Value>
class BST{
private:
    struct Node{
       Key key;
       Value value;
       Node *left;
       Node *right;

       Node(Key key,Value value){
           this->key = key;
           this->value = value;
           this->left = this->right = NULL;
       }
    };
    Node *root;
    int count;

public:
    BST(){
        root=NULL;
        count=0;
    }
    ~BST(){
        //todo
    }
    int size(){
        return count;
    }
    bool isEmpty(){
        return count==0;
    }
    void insert(Key key,Value value){
        root = insert(root,key,value)
    }
private:
    //向以node为根的二叉搜索树中，插入节点（key,value）
    //返回插入新节点后的二叉搜索树的根
    Node* insert(Node *node,Key key,Value value){
        if(node==NULL){
            count ++;
            return new Node(key,value);
        }
        if(key==node->key)
            node->value = value;
        else if(key <node->key)
            node->left = insert(node->left,key,value);
        else
            node->right = insert(node->right,key,value)
        return node;
    }
    
};