POJ 3660 Cow ContestCow（Floyd传递闭包）题解

题意：给出m个关系，问你能确定机头牛的排名

思路：要确定排名那必须要把他和其他n-1头牛比过才行，所以Floyd传递闭包，如果赢的+输的有n-1就能确定排名。

代码：

#include<cstdio>
#include<set>
#include<map>
#include<cmath>
#include<stack>
#include<vector>
#include<queue>
#include<cstring>
#include<string>
#include<sstream>
#include<iostream>
#include<algorithm>
#define ll long long
using namespace std;
const int maxn = +;
const int INF = 0x3f3f3f3f;
int mp[maxn][maxn],can[maxn];
int main(){
    int n,m;
    memset(mp,,sizeof(mp));
    memset(can,,sizeof(can));
    scanf("%d%d",&n,&m);
    while(m--){
        int u,v;
        scanf("%d%d",&u,&v);
        mp[u][v] = ;
    }
    for(int k = ;k <= n;k++){
        for(int i = ;i <= n;i++){
            for(int j = ;j <= n;j++){
                if(mp[i][k] && mp[k][j]){
                    mp[i][j] = ;
                }
            }
        }
    }
    int ans = ;
    for(int i = ;i <= n;i++){
        for(int j = ;j <= n;j++){
            if(mp[i][j] && i != j){
                can[i]++;
                can[j]++;
            }
        }
    }
    for(int i = ;i <= n;i++){
        if(can[i] == n - ) ans++;
    }
    printf("%d\n",ans);
    return ;
}