优先队列水过：

#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    priority_queue<int,vector<int>,greater<int> > q;
    cin>>n;
    for(int i=1;i<=n;i++){
        int op,x;
        cin>>op;
        if(op==1){
            cin>>x;
            q.push(x);
        }
        if(op==2){
            cout<<q.top()<<endl;
        }
        if(op==3){
            q.pop();
        }
    }
}

手写堆：

#include<bits/stdc++.h>
using namespace std;
const int N=1e6+5;
int len,heap[N];
void push(int x){
    heap[++len]=x;
    int i=len;
    while(i>1&&heap[i]<heap[i/2]){
        swap(heap[i],heap[i/2]);
        i=i/2;
    }
}
void pop(){
    heap[1]=heap[len--];
    int i=1;
    while(2*i<=len){
        int son=2*i;
        if(son<len&&heap[son+1]<heap[son]){
            son++;
        }
        if(heap[son]<heap[i]){
            swap(heap[son],heap[i]);
            i=son;
        }
        else{
            break;
        }
    }
}
int main(){
    int n;
    cin>>n;
    while(n--){
        int x,y;
        cin>>x;
        if(x==1){
            cin>>y;
            push(y);
        }
        if(x==2){
            cout<<heap[1]<<endl;
        }
        if(x==3){
            pop();
        }
    }
    return 0;
}

STL

#include<bits/stdc++.h>
#include <queue>
using namespace std;
priority_queue<int,vector<int>,greater<int> > q;
int n,x,y;
int main(){
    cin>>n;
    while(n--){
        cin>>x;
        if(x==1){
            cin>>y;
            q.push(y);
        }
        if(x==2){
            cout<<q.top()<<endl;
        }
        if(x==3){
            q.pop();
        }
    }
    return 0;
}