poj 1789 Truck History

题目连接：http://poj.org/problem?id=1789

每条边的权值为任意两truck不相等字母的数量，求最小生成树

代码：

#include <iostream>
#include <stdio.h>
#include <string.h>
#define max 1000000
using namespace std;
int map[2005][2005];
int ans;
void prim(int n)
{
    int i,pre,j,min;
    int vis[2005] = {0};
    int d[2005];
    for(i = 1;i < n;i++)
    d[i] = map[0][i];

    vis[0] = 1;

    for(i = 1;i < n;i++)
    {
        min = max;
        for(j = 1;j < n;j++)
        {
            if(min > d[j] && !vis[j])
            min = d[j],pre = j;
        }
        ans += min;
        vis[pre] = 1;
        for(j = 1;j < n;j++)
        {
            if(d[j] > map[pre][j] && !vis[j])
            d[j] = map[pre][j];
        }

    }
    return ;
}
int main()
{
    int n,i,j;

    char s[2005][10];
    while(scanf("%d",&n)&&n)
    {
        for(i = 0;i < n;i++)
        cin>>s[i];

        for(i = 0;i < n;i++)
        {
            for(j = 0;j < n;j++)
            {
                int w;
                w = 0;
                for(int k = 0;k < 7;k++)
                if(s[i][k] != s[j][k])
                w++;
                map[i][j] = w;
            }
        }

        ans = 0;
        prim(n);
        cout << "The highest possible quality is 1/"<< ans << "."<<endl;
    }
    return 0;
}