hdu 2647(拓扑排序，判断有向图是否存在回路及自环，并统计每个顶点的前驱点数)

/*
  Name: 拓扑排序，判断有向图是否存在回路及自环，并统计每个顶点的前驱点数 
  Copyright: 
  Author: Try86
  Date: 15/04/12 22:25
  Description: 
*/

#include <queue>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>

using namespace std;

const int N = 10005;

int sum, flag;
int counts[N];
struct node {
    int v;
    node *next;
    node(int vv, node *p) {
        v = vv;
        next = p;
    }
};
struct graph {
    int inDeg; //统计入度数 
    node *link;
}G[N];

void init(int n) {
    for (int i=1; i<=n; ++i) {
        G[i].inDeg = 0;
        G[i].link = NULL;
        counts[i] = 0;
    }
    return ;
} 

void buildG(int u, int v) {
    node *p = new node(v, G[u].link);
    G[u].link = p;
    ++G[v].inDeg;
    return ;
}

void topoSort(int n) {
    sum = 0;
    flag = true;
    queue<int> Q;
    for (int i=1; i<=n; ++i) {//入度数为0的点入队列 
        if (G[i].inDeg == 0) Q.push(i), --G[i].inDeg;
    }
    while (!Q.empty()) {
        int u = Q.front();
        sum += counts[u];  //统计所有点的总的前驱点数 
        Q.pop();
        for (node *p=G[u].link; p; p=p->next) {
            --G[p->v].inDeg;  //与u邻接的点的入度数减1 
            if (G[p->v].inDeg == 0) {
                Q.push(p->v);
                counts[p->v] = counts[u] + 1;//统计点v的前驱点数 
            }
        }
    }
    for (int i=1; i<=n; ++i) {//判断是否有回路或自环 
        if (G[i].inDeg > 0) {
            flag = false;
            break;
        }
    }
    return ;
}

void del(node *p) {
    if (!p) return ;
    del(p->next);
    delete p;
    return ;
}

int main() {
    int n, m;
    while (scanf("%d%d", &n, &m) != EOF) {
        init(n);
        int u, v;
        for (int i=0; i<m; ++i) {
            scanf ("%d%d", &u, &v);
            buildG(v, u);  //注意建图的顶点顺序 
        }
        topoSort(n);
        if (flag) printf ("%d\n", 888*n+sum);
        else printf ("-1\n");
        for (int i=1; i<=n; ++i) del(G[i].link);
    }
    return 0;
}