这也能AC

#include <bits/stdc++.h>
using namespace std;
struct stu{
	string name;
	int score;
}b[1000005],a;
int n,c,x,f=1,y;
int main(){
	cin>>n;
	while(n--){
		cin>>c;
		if(c==1){
			f=1;
			cin>>a.name>>a.score;
			for(int i=1;i<=x;i++){
				if(b[i].name==a.name){
					b[i].score=a.score;
					f=0;
					break;
				}
			}
			if(f){
				b[++x]=a; 
				y++;
			}
			cout<<"OK\n";
		}else if(c==2){
			f=1;
			cin>>a.name;
			for(int i=1;i<=x;i++){
				if(b[i].name==a.name){
					cout<<b[i].score<<endl;
					f=0;
					break;
				}
			}
			if(f) cout<<"Not found"<<endl;
		}else if(c==3){
			f=1;
			cin>>a.name;
			for(int i=1;i<=x;i++){
				if(b[i].name==a.name){
					b[i].name="";
					b[i].score=-1;
					y--;
					cout<<"Deleted successfully"<<endl;
					f=0;
					break;
				}
			}
			if(f) cout<<"Not found"<<endl;
		}else if(c==4){
			cout<<y<<endl;
		}
	}
    return 0;
}