csu oj Infected Computer 1427

#include <iostream>
#include <algorithm>
#include <stdio.h>
#define max 20005
#define ll long long
using namespace std;

struct G{
    int from;
    int to;
    ll time;
}game[max];

bool graf[max];

bool cmp(G a,G b){
    return a.time < b.time;
}
int main()
{
    int n,m;
    while(cin>>n>>m){
        for(int i = 0;i < max;i++){
            graf[i]=false;
            game[i].time=game[i].from=game[i].to=0;
        }
        graf[1]=true;

        for(int i = 0;i < m;i++){
            cin>>game[i].time>>game[i].from>>game[i].to;
        }
        sort(game,game+m,cmp);

        bool flag = false;
        for(int i = 0;i < m;i++){
            if(game[i].from==1){
                flag = true;
                //graf[game[i].to] = true;
            }
            if(flag&&graf[game[i].from]){
                graf[game[i].to] = true;
            }
        }
        ll ans = 0;
        for(int i = 1;i <= n;i++){
            if(graf[i])ans++;
        }
        cout<<ans<<endl;
    }
    return 0;
}

如果非要给划分，我想应该是属于并查集一类的