（最小生成树）Truck History --POJ -- 1789

链接：

http://poj.org/problem?id=1789

代码：

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <iostream>
#include <algorithm>
using namespace std;

const int N = 2005;
const int INF = 0xfffffff;

int n;
int J[N][N], dist[N];
char s[N][10];
bool vis[N];

int Len(char a[], char b[])
{
    int ans=0;

    for(int i=0; i<7; i++)
    {
       if(a[i]!=b[i])
        ans++;
    }
    return ans;
}

int Prim()
{
    int i, j, ans=0;

    memset(vis, 0, sizeof(vis));
    vis[1]=1;

    dist[1]=0;
    for(i=1; i<=n; i++)
        dist[i]=J[1][i];

    for(i=1; i<n; i++)
    {
        int MIN=INF;
        int index=1;
        for(j=1; j<=n; j++)
        {
            if(!vis[j] && dist[j]<MIN)
            {
                index=j;
                MIN=dist[j];
            }
        }
        vis[index]=1;
        if(MIN==INF)
            break;
        ans += MIN;

        for(j=1; j<=n; j++)
        {
            if(!vis[j] && dist[j]>J[index][j] && J[index][j]>0 )
                dist[j]=J[index][j];
        }
    }

    return ans;
}

int main ()
{

    while(scanf("%d", &n), n)
    {
        int i, j;

        memset(s, 0, sizeof(s));
        for(i=1; i<=n; i++)
            scanf("%s", s[i]);

        for(i=1; i<=n; i++)
        for(j=1; j<=i; j++)
        {
            J[i][j]=J[j][i]=Len(s[i], s[j]);
        }

        int ans=Prim();
        printf("The highest possible quality is 1/%d.\n", ans);
    }
    return 0;
}