839. 模拟堆 题解

#include <iostream>
using namespace std;
const int N = 100010;

int n, k, x, len, m;
int h[N], ph[N], hp[N];
string op;

void heap_swap(int a, int b)
{
    swap(ph[hp[a]], ph[hp[b]]);
    swap(hp[a], hp[b]);
    swap(h[a], h[b]);
}

void up(int u)
{
    while (u / 2 && h[u / 2] > h[u])
    {
        heap_swap(u / 2, u);
        u /= 2;
    }
}

void down(int u)
{
    int t = u;
    if (u * 2 <= len && h[u * 2] < h[t]) t = u * 2;
    if (u * 2 + 1 <= len && h[u * 2 + 1] < h[t]) t = u * 2 + 1;
    
    if (u != t)
    {
        heap_swap(u, t);
        down(t);   
    }
}

int main()
{
    cin >> n;

    for(int i = 1; i <= n; i++)
    {
        cin >> op;
        if (op == "I")
        {
            cin >> x;
            len++, m++;
            ph[m] = len, hp[len] = m;
            h[len] = x;
            up(len);
        }
        else if (op == "PM")    cout << h[1] << endl;
        else if (op == "DM")
        {
            heap_swap(1, len);
            len--;
            down(1);
        }
        else if (op == "D")
        {
            cin >> k;
            k = ph[k];
            heap_swap(k, len);
            len--;
            down(k), up(k);
        }
        else 
        {
            cin >> k >> x;
            k = ph[k];
            h[k] = x;
            down(k), up(k);
        }
    }
    return 0;
}