poj3683 Priest John's Busiest Day

不用topsort的，我也不知道为啥。

#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;
struct Node{
    int fro, too;
}nd[2005];
struct Edge{
    int too, nxt, val;
}edge[4000005];
int uu, vv, ww, n, hea[2005], cnt, dfn[2005], loo[2005], scc, bel[2005];
int sta[2005], din, ind;
bool ins[2005];
bool pd(int x, int y){
    if(nd[x].fro<=nd[y].fro && nd[x].too>nd[y].fro) return true;
    swap(x, y);
    if(nd[x].fro<=nd[y].fro && nd[x].too>nd[y].fro) return true;
    return false;
}
void add_edge(int fro, int too){
    edge[++cnt].nxt = hea[fro];
    edge[cnt].too = too;
    hea[fro] = cnt;
}
void tarjan(int u){
    dfn[u] = loo[u] = ++ind;
    sta[++din] = u;
    ins[u] = true;
    for(int i=hea[u]; i; i=edge[i].nxt){
        int t=edge[i].too;
        if(!dfn[t]){
            tarjan(t);
            loo[u] = min(loo[u], loo[t]);
        }
        else if(ins[t]) loo[u] = min(loo[u], dfn[t]);
    }
    int j;
    if(dfn[u]==loo[u]){
        scc++;
        do{
            j = sta[din--];
            ins[j] = false;
            bel[j] = scc;
        }while(dfn[j]!=loo[j]);
    }
}
int main(){
    cin>>n;
    for(int i=0; i<n; i++){
        scanf("%d:%d", &uu, &vv);
        uu = uu * 60 + vv;
        scanf("%d:%d", &vv, &ww);
        vv = vv * 60 + ww;
        scanf("%d", &ww);
        nd[2*i].fro = uu, nd[2*i].too = uu + ww;
        nd[2*i+1].fro = vv - ww, nd[2*i+1].too = vv;
    }
    for(int i=0; i<n+n; i++)
        for(int j=i+1; j<n+n; j++)
            if(pd(i, j)){
                add_edge(i, j^1);
                add_edge(j, i^1);
            }
    for(int i=0; i<n+n; i++)
        if(!dfn[i])
            tarjan(i);
    for(int i=0; i<n+n; i+=2)
        if(bel[i]==bel[i^1]){//说明以前有要求既不能选i又不能选i^1
            printf("NO\n");
            return 0;
        }
    printf("YES\n");
    for(int i=0; i<n+n; i+=2){
        int id=bel[i]<bel[i^1]?i:i+1;//为什么要这样做？id小说明先求出来，在图里是靠近下游的，影响小
        printf("%02d:%02d %02d:%02d\n", nd[id].fro/60, nd[id].fro%60, nd[id].too/60, nd[id].too%60);
    }
    return 0;
}

poj3683 Priest John's Busiest Day