Poj3660 Cow Contest(Floyd)

题意：

给出n的牛的m轮比赛结果，计算有几头牛的排名已经可以确定。

思路：

Floyd跑一遍，然后判断每个牛，如果他和别人都有比赛，那么它排名可定。

#include <cstdio>
#include <cstring>
#include <queue>
#include <algorithm>
#pragma comment(linker, "/STACK:102400000,102400000")
typedef long long LL;
const int INF = 0x3f3f3f3f;
const int maxn = 100+5;
using namespace std;

int n,m;
int G[maxn][maxn];

void Floyd(){
	for(int k = 1; k <= n; ++k){
		for(int i = 1; i <= n; ++i){
			for(int j = 1; j <= n; ++j){
				G[i][j] = G[i][j]||(G[i][k]&&G[k][j]);
			}
		}
	}
}

int main()
{
    //freopen("in.txt","r",stdin);
    
	while(scanf("%d%d",&n,&m) == 2){
		memset(G, 0, sizeof(G));
		for(int i = 1; i <= n; ++i) G[i][i] = 1;
		
		for(int i = 0; i < m; ++i){
			int a,b; scanf("%d%d",&a,&b);
			G[a][b] = 1;
		}
		
		Floyd();
		
		int ans = 0;
		for(int i = 1; i <= n; ++i){
			bool flag = true;
			for(int j = 1; j <= n; ++j) if(!G[j][i]&&!G[i][j]) {flag = false; break; }
			if(flag) ++ans;
		}
		printf("%d\n",ans);
	}
    fclose(stdin);
	return 0;
}