bzoj1612: [Usaco2008 Jan]Cow Contest奶牛的比赛

#include <bits/stdc++.h>
#define eps 1e-8
#define ll long long
#define INF 2147483647
#define ll_INF 9223372036854775807
using namespace std;
inline int read() {
	int x = 0,tmp = 1;char ch = getchar();
	while( ch < '0' || ch > '9' ) {if ( ch == '-' ) tmp = -1; ch = getchar();}
	while( ch >= '0' && ch <= '9'){x = x * 10 + ch - '0'; ch = getchar(); }
	return x * tmp;
}
bool _edge[110][110];
int main() {
	memset( _edge, 0, sizeof( _edge ) );
	int N = read(), M = read();
	for( int i = 1 ; i <= M ; ++ i ) {
		int u = read(), v = read();
		_edge[u][v] = 1;
	}
	for( int k = 1 ; k <= N ; ++ k )
		for( int i = 1 ; i <= N ; ++ i )
			for( int j = 1 ; j <= N ; ++ j )
				_edge[i][j] = ( _edge[i][k] && _edge[k][j] ) || _edge[i][j];
	
	int ans = 0;
	for( int i = 1 ; i <= N ; ++ i ) {
		int cnt = 0;
		for( int j = 1 ; j <= N ; ++ j ) cnt += _edge[j][i];
		for( int j = 1 ; j <= N ; ++ j ) cnt += _edge[i][j];
		ans += ( cnt == N - 1 );
	} 
	printf( "%d\n", ans );

	return 0;
}