POJ 1975 Median Weight Bead (Floyd)

Median Weight Bead

Time Limit: 1000MS		Memory Limit: 30000K
Total Submissions: 2494		Accepted: 1249

Description

There are N beads which of the same shape and size, but with different weights. N is an odd number and the beads are labeled as 1, 2, ..., N. Your task is to find the bead whose weight is median (the ((N+1)/2)th among all beads). The following comparison has been performed on some pairs of beads: 
A scale is given to compare the weights of beads. We can determine which one is heavier than the other between two beads. As the result, we now know that some beads are heavier than others. We are going to remove some beads which cannot have the medium weight. 

For example, the following results show which bead is heavier after M comparisons where M=4 and N=5. 

1.	Bead 2 is heavier than Bead 1.

2.	Bead 4 is heavier than Bead 3.

3.	Bead 5 is heavier than Bead 1.

4.	Bead 4 is heavier than Bead 2.

From the above results, though we cannot determine exactly which is the median bead, we know that Bead 1 and Bead 4 can never have the median weight: Beads 2, 4, 5 are heavier than Bead 1, and Beads 1, 2, 3 are lighter than Bead 4. Therefore, we can remove these two beads. 

Write a program to count the number of beads which cannot have the median weight. 

Input

The first line of the input file contains a single integer t (1 <= t <= 11), the number of test cases, followed by the input data for each test case. The input for each test case will be as follows: 
The first line of input data contains an integer N (1 <= N <= 99) denoting the number of beads, and M denoting the number of pairs of beads compared. In each of the next M lines, two numbers are given where the first bead is heavier than the second bead. 

Output

There should be one line per test case. Print the number of beads which can never have the medium weight.

Sample Input

1
5 4
2 1
4 3
5 1
4 2

Sample Output

2

Source

Tehran Sharif 2004 Preliminary

 

 

题意：有n个bead 给出m种轻重关系 求有多少人bead肯定不可能是 in the median weight

思路： floyd 求出每个bead 与其它bead的关系 1表示比其它的重，-1表示轻于其它的。
如果它重于其它的个数，或轻于其它的个数超过一半 那它就不可能是中间的

 

 

#include<iostream>
#include<cstdio>
#include<cstring>

using namespace std;

const int N=110;

int map[N][N];

int main(){

    //freopen("input.txt","r",stdin);

    int t,n,m;
    scanf("%d",&t);
    while(t--){
        scanf("%d%d",&n,&m);
        int a,b;
        int i,j,k;
        memset(map,0,sizeof(map));
        for(i=0;i<m;i++){
            scanf("%d%d",&a,&b);
            map[a][b]=1;
            map[b][a]=-1;
        }
        for(k=1;k<=n;k++)
            for(i=1;i<=n;i++)
                for(j=1;j<=n;j++){
                    if(map[i][k]==1 && map[k][j]==1)
                        map[i][j]=1;
                    if(map[i][k]==-1 && map[k][j]==-1)
                        map[i][j]=-1;
                }
        int ans=0;
        for(i=1;i<=n;i++){
            a=0,b=0;
            for(j=1;j<=n;j++){
                if(map[i][j]==1)
                    a++;
                if(map[i][j]==-1)
                    b++;
            }
            if(a>=(n+1)/2 || b>=(n+1)/2)
                ans++;
        }
        printf("%d\n",ans);
    }
    return 0;
}