POJ 3660 Cow Contest (floyd 传递闭包)

题目地址：点击打开链接

题意：有n头牛，有强有弱，现在给出m个关系A B（表示A比B强），现在让你求有几头牛的排名是可以确定的。

思路：强弱关系是传递的，先求一次传递闭包，再枚举每头牛，若比他强的加上比他弱的牛数量为n-1，那么他的名

次就是确定的。

#include<iostream>#include<cstdio>#include<cstring>using namespace std;const int maxn = 105;int link[maxn][maxn], n, m;void floyd(){    for(int k = 1; k <= n; k++)        for(int i = 1; i <= n; i++)            if(link[i][k])                for(int j = 1; j <= n; j++)                    if(link[k][j])                        link[i][j] = 1;}int solve(){    int res = 0;    for(int i = 1; i <= n; i++)    {        int cnt = 0;        for(int j = 1; j <= n; j++)        {            if(link[i][j]) cnt++;            if(link[j][i]) cnt++;        }        if(cnt == n-1) res++;    }    return res;}int main(void){    while(cin >> n >> m)    {        memset(link, 0, sizeof(link));        while(m--)        {            int u, v;            scanf("%d%d", &u, &v);            link[u][v] = 1;        }        floyd();        printf("%d\n", solve());    }    return 0;}

Cow Contest

Time Limit: 1000MS Memory Limit: 65536KTotal Submissions: 10967 Accepted: 6105

Description

N (1 ≤ N ≤ 100) cows, conveniently numbered 1..N, are participating in a programming contest. As we all know, some cows code better than others. Each cow has a certain constant skill rating that is unique among the competitors.

The contest is conducted in several head-to-head rounds, each between two cows. If cow A has a greater skill level than cow B (1 ≤ A ≤ N; 1 ≤ B ≤ N; A ≠ B), then cow A will always beat cow B.

Farmer John is trying to rank the cows by skill level. Given a list the results of M (1 ≤ M ≤ 4,500) two-cow rounds, determine the number of cows whose ranks can be precisely determined from the results. It is guaranteed that the results of the rounds will not be contradictory.

Input

* Line 1: Two space-separated integers: N and M
* Lines 2..M+1: Each line contains two space-separated integers that describe the competitors and results (the first integer, A, is the winner) of a single round of competition: A and B

Output

* Line 1: A single integer representing the number of cows whose ranks can be determined
　

Sample Input

5 54 34 23 21 22 5

Sample Output

2