POJ 1789 Truck History

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

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#define INF 0x0fffffff
int mat[2002][2002];
int N;
typedef struct Code {
    char str[10];
}Code;
Code codes[2002];
int calc(char *str1,char *str2)
{
    char *p=str1,*q=str2;
    int count=0;
    while(*p&&*q) {
        if((*p)!=(*q))
            count++;
        p++;
        q++;
    }
    return count;
}
int prim()
{
    int start=0;
    bool visited[2002]={false};
    int nearest[2002];
    int min_cost=0;
    int min=INF;
    int pos;
    int i,j;
    for(i=0;i<N;i++)
        nearest[i]=mat[start][i];
    visited[start]=true;
    nearest[start]=0;
    for(i=1;i<N;i++) {
        min=INF;
        for(j=0;j<N;j++) {
            if(!visited[j]&&nearest[j]<min) {
                min=nearest[j];
                pos=j;
            }
        }
        min_cost+=min;
        visited[pos]=true;
        for(j=0;j<N;j++)
            if(!visited[j]&&nearest[j]>mat[pos][j])
                nearest[j]=mat[pos][j];
    }
    return min_cost;
}
int main()
{
    while(scanf("%d",&N)!=EOF) {
        if(N==0)
            return 0;
        int i,j;
        for(i=0;i<N;i++) {
            scanf("%s",codes[i].str);
        }
        for(i=0;i<N;i++)
            for(j=0;j<=i;j++)
                if(i==j)
                    mat[i][j]=INF;
                else mat[j][i]=mat[i][j]=calc(codes[i].str,codes[j].str);
        printf("The highest possible quality is 1/%d.\n",prim());
    }
    return 0;
}