HDU2647+拓扑排序

先判断是否存在环。。然后dfs出每个人比几个人要求高。。

///*
//拓扑
//*/
#include<stdio.h>
#include<string.h>
const int maxn =  10105;
int ind[ maxn ],add[ maxn ],vis[ maxn ];
struct node{
    int u,next;
}edge[ maxn<<2 ];
int cnt,head[ maxn ];
void init(){
    cnt = 0;
    memset( add,0,sizeof( add ) );
    memset( head,-1,sizeof( head ) );
    memset( vis,0,sizeof( vis ) );
    memset( ind,0,sizeof( ind ) );
}
void addedge( int a,int b ){
    edge[ cnt ].u = b;
    edge[ cnt ].next = head[ a ];
    head[ a ] = cnt++;
}

int dfs( int cur ){
    if( vis[ cur ]!=0 ) return add[ cur ];
    //printf("cur=%d\n",cur);
    vis[ cur ] = 1;
    for( int i=head[ cur ];i!=-1;i=edge[ i ].next ){
        //printf("nxt=%d\n",edge[i].u);
        int dis = dfs( edge[ i ].u );
        if( add[ cur ]<dis+1 ) add[ cur ] = dis+1;
    }
    return add[ cur ];
}

int tuopu( int n ){
    int cnt = 0;
    for( int i=1;i<=n;i++ ){
        int s = -1;
        for( int j=1;j<=n;j++ ){
            if( ind[ j ]<-1){
                return -1;
            }
            if( ind[ j ]==0 ){
                ind[ j ] = -1;
                s = j;
                cnt++;
                break;
            }
        }
        //printf("s=%d\n",s);
        if( s==-1 ) break;
        for( int j=head[ s ];j!=-1;j=edge[ j ].next ){
            ind[ edge[j].u ]--;
            if( ind[ edge[j].u ]<-1 ) return -1;
        }
    }
    if( cnt==n ) return 1;
    else return -1;
}

int main(){
    int n,m;
    while( scanf("%d%d",&n,&m)==2 ){
        init();
        int a,b;
        while( m-- ){
            scanf("%d%d",&a,&b);
            ind[ b ]++;
            addedge( a,b );
        }

        int flag = tuopu( n );
        if( flag==-1 ){
            printf("-1\n");
            continue;
        }
        //printf("flag=%d\n",flag);
        for( int i=1;i<=n;i++ ){
            if( vis[ i ]==0 ){
                dfs( i );
            }
        }
        int sum = n*888;
        //printf("sum=%d\n",sum);
        for( int i=1;i<=n;i++ ){
            sum+=add[i];
            //printf("add[%d]=%d\n",i,add[i]);
        }
        printf("%d\n",sum);
    }
    return 0;
}