hdu2647拓扑排序（逆向）

/*****************************************
Author      :Crazy_AC(JamesQi)
Time        :2015
File Name   :
*****************************************/
// #pragma comment(linker, "/STACK:1024000000,1024000000")
#include <iostream>
#include <algorithm>
#include <iomanip>
#include <sstream>
#include <string>
#include <stack>
#include <queue>
#include <deque>
#include <vector>
#include <map>
#include <set>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
#include <limits.h>
using namespace std;
#define MEM(a,b) memset(a,b,sizeof a)
typedef long long LL;
typedef unsigned long long ULL;
typedef pair<int,int> ii;
const int inf = 1 << 30;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;
int n,m;
int in[10010];
vector<int> G[10010];
inline void Init(){
MEM(in, 0);
for (int i = 1;i <= n;i++)
G[i].clear();
}
void Topo(){
int cnt = 0;
int times = 0;
int sum = 0;
bool flag = true;
int ss = 888;
while(true){
queue<int> que;
int rec = 0;
for (int i = 1;i <= n;i++){
if (in[i] == 0){
que.push(i);
in[i]--;
cnt++;
rec++;
// cout << "i = " << i << endl;
}
}
sum += (rec * ss);
ss++;
if (que.empty() && cnt < n) {
flag = false;
break;
}
if (cnt == n) break;
while(!que.empty()){
int u = que.front();
que.pop();
for (int i = 0;i < G[u].size();i++){
int v = G[u][i];
in[v]--;
}
}
// sum += (rec * 888);
}
if (!flag) printf("-1\n");
else printf("%d\n",sum);
}
int main()
{
// freopen("in.txt","r",stdin);
// freopen("out.txt","w",stdout);
while(~scanf("%d%d",&n,&m)){
Init();
int u,v;
for (int i = 1;i <= m;i++){
scanf("%d%d",&u,&v);
in[u]++;
G[v].push_back(u);
}
Topo();
}
return 0;
}