uestc 方老师的分身 III 拓扑排序

没什么好说的。。

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<string>
#include<queue>
#include<algorithm>
#include<map>
#include<iomanip>
#include<climits>
#include<string.h>
#include<cmath>
#include<stdlib.h>
#include<vector>
#define INF 1e7
#define MAXN 100010
#define maxn 1000010
#define Mod 1000007
#define N 1010
using namespace std;
typedef long long LL;

int n, m;
int son[10001];
int ans[10001];

void init()
{
    memset(son,0,sizeof(son));
    memset(ans,0,sizeof(ans));
}

void process()
{
    vector<int> G[10010];
    int x, y;
    init();
    for (int i = 0; i < m; ++i) {
        cin >> x >> y;
        G[y].push_back(x);
        son[x]++;
    }
    queue<int> q;
    for (int i = 1; i <= n; ++ i)
        if (son[i] == 0){
            q.push(i);
            ans[i] = 888;
        }
    int res = n;
    while (!q.empty()) {
        int t = q.front();
        q.pop();
        res--;
        for (int i = 0; i < G[t].size(); ++i) {
            int v = G[t][i];
            if (--son[v] == 0) {
                ans[v] = ans[t] + 1;
                q.push(v);
            }
        }
    }
    if (res > 0) puts("-1");
    else {
        int sum = 0;
        for (int i = 1; i <= n; ++i)
            sum += ans[i];
        cout << sum << endl;
    }
}

int main()
{
    while (cin >> n >> m)
        process();
    return 0;
}