P1983 [NOIP2013 普及组] 车站分级

https://www.luogu.com.cn/problem/P1983

思路

https://www.cnblogs.com/tomori/p/14331510.html

Code

https://www.luogu.com.cn/record/103494700

参考：

https://marhoosh.github.io/2021/10/29/%E6%8B%93%E6%89%91%E6%8E%92%E5%BA%8F/#

#include <iomanip>
#include <bits/stdc++.h>
#include <iostream>
using namespace std;
#include <limits.h>
#include <math.h>
#include <vector>
#include <set>
#include <map>
#include <stack>
#include <queue>

/*
https://atcoder.jp/contests/abcxxx/tasks/abcxxx_d
*/

typedef long long ll;

int n, m;

const long long maxn=1e3+11;
long long gra[maxn][maxn],is[maxn],dr[maxn],vis[maxn];

int main()
{
    cin >> n >> m;
    for(ll i=1;i<=m;i++){
        memset(is,0,sizeof(is));
        ll s;

        cin>>s;
        
        ll st[maxn];
        for(ll j=0;j<s;j++){
            cin>>st[j];
            is[st[j]]=1;
        }
        
        for(ll j=st[0];j<=st[s-1];j++){
            if(!is[j]){
                for(ll k=0;k<s;k++){
                    if(!gra[j][st[k]]){
                        gra[j][st[k]]=1;
                        dr[st[k]]++;
                    }  
                }
            }
        }
    }
    
    int level = 0;

    do{
        vector<int> stops;

        for(int i=1; i<=n; i++){
            if (dr[i] == 0 && !vis[i]){
                stops.push_back(i);
                vis[i] = true;
            }
        }
        
//        cout << "stops.size() =" << stops.size() << endl;

        if (stops.size() == 0){
            break;
        }

        level++;
        
        for(int i=0; i<stops.size(); i++){
            for(ll j=1;j<=n;j++){
                if(gra[stops[i]][j]){
                    gra[stops[i]][j]=0;
                    dr[j]--;
                }
            }
        }
    }while(true);
    
    cout << level << endl;

    return 0;
}