HDU2647

第一道逆拓扑纪念一下。。。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<string.h>
#define maxint 999999999
#define MAXN 10005
#define ll long long
using namespace std;

int n,m,k,flag,num;
ll sum;
int Mark[MAXN],st[MAXN],vis[MAXN];
struct node{
     int x,y;
     int flag;
}cmp[];

void topsort(){
    int l=;
    while(){
        int j;
        int s=;
        for(j=;j<=n;j++){
            if(Mark[j]==){
                sum+=num;
                --Mark[j];
                ++s;
                vis[s]=j;
                ++l;
            }
        }
        num++;
        if(l==n)
           break;
        if(!s){
            flag=;
            break;
        }
        else{
            for(int i=;i<=s;i++){
            for(int k=;k<=m;k++){
                if(cmp[k].y==vis[i]&&Mark[cmp[k].x]!=&&cmp[k].flag==){
                    --Mark[cmp[k].x];
                    cmp[k].flag=;
                }
            }
            }
        }
    }
}

int main()
{

    while(scanf("%d %d",&n,&m)!=EOF){
        sum=;
        num=;
        memset(vis,,sizeof(vis));
        memset(Mark,,sizeof(Mark));
        for(int i=;i<=m;i++){
            scanf("%d %d",&cmp[i].x,&cmp[i].y);
                ++Mark[cmp[i].x];
                cmp[i].flag=;
        }
        flag=;
        topsort();
        if(flag)
            printf("-1\n");
        else
          printf("%lld\n",sum);
    }return ;
}