写法比较简单，码量不大，题目不难，纯模拟。最多map，本人代码如下。

#include<bits/stdc++.h>
using namespace std;
map<string,long long>h;
map<string,bool>m;
int main(){
	long long a,b,c,d,e=0;
	string bb;
	cin>>a;
	for(int i=1;i<=a;i++){
		cin>>b;
		if(b==1){
			cin>>bb;
			cin>>c;
			h[bb]=c;
			cout<<"OK"<<endl;
			if(m[bb]==0){
				e++;
			}
			m[bb]=1;
			continue;
		}
		if(b==2){
			cin>>bb;
			if(m[bb]==1){
				cout<<h[bb]<<endl; continue;
			}else{
				cout<<"Not found"<<endl; continue;
			}
		}
		if(b==3){
			cin>>bb;
			if(m[bb]==1){
				cout<<"Deleted successfully"<<endl;
					e--;
				m[bb]=0;
				continue;
			}else{
				cout<<"Not found"<<endl;continue;
			}	
		}
		if(b==4){
			cout<<e<<endl;
			continue;
		}

	}
	return 0;
}