hdu 2647 Reward 拓扑排序入门

#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<vector>
#include<queue>

using namespace std;

#define N 10005

vector<int> v
;

int dep
, vis
, in
;
queue<int> q;

int n, m;
bool ok;

void init()
{
	memset( dep, 0, sizeof(dep) );
	memset( in, 0, sizeof(in) );
	for( int i = 1; i <= n; i ++ )
	{
		v[i].clear();
	}
	ok = 0;
}

void bfs( int u )
{
	while(!q.empty())
		q.pop();
	memset(vis, 0, sizeof(vis));
	q.push(u);
	vis[u] = 1;
	while( !q.empty() )
	{
		int x = q.front();
		q.pop();
		for ( int i = 0; i < v[x].size(); i++ )
		{
			int to = v[x][i];
			if( vis[to] )
			{
				ok = 1;
				return;
			}
			dep[to] = max(dep[x] + 1, dep[to]);
			q.push(to);
		}
	}
}

int main()
{
	while( ~scanf("%d%d", &n, &m) )
	{
		init();
		int a, b;
		for ( int i = 1; i <= m; i++ )
		{
			scanf("%d%d", &a, &b);
			in[a] = 1;
			v[b].push_back(a);
		}
		for ( int i = 1; i <= n; i ++ )
		{
			if(ok)
				break;
			bfs(i);
		}
		
		if(ok)
		{
			printf("-1\n");
		}
		else
		{
			int ans = 0;
			for ( int i = 1; i <= n; i++ )
			{
				ans += 888 + dep[i];
			}
			printf("%d\n", ans);
		}
	}
	return 0;
}

/*

4 4
1 2
1 3
1 4
2 4

4 4
1 2
1 3
1 4
2 3

output:3555
*/