POJ1789 Truck History 最小生成树

计算整个汽车演化过程中所要改变的最少的字符数。改变的字符数的计算方式为1-7位不同位的个数。

代码如下：

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

int N, pos, set[2005];

char s[2005][10];

struct Node
{
    int x, y, diff;
    bool operator < (Node t) const
    {
        return diff < t.diff;
    }
}e[4000005];

int diff(int x, int y)
{
    int cnt = 0;
    for (int i = 0; i < 7; ++i) {
        if (s[x][i] != s[y][i]) {
            ++cnt;
        }
    }
    return cnt;
}

int find(int x)
{
    return set[x] = x == set[x] ? x : find(set[x]);
}

void merge(int x, int y) 
{
    set[x] = y;
}

int main()
{
    int a, b, ans, cnt;
    while (scanf("%d", &N), N) {
        pos = ans = cnt = 0;
        for (int i = 1; i <= N; ++i) {
            scanf("%s", s[i]); 
            set[i] = i;
        }
        for (int i = 1; i <= N; ++i) {
            for (int j = i+1; j <= N; ++j) {      
                ++pos;
                e[pos].x = i, e[pos].y = j;
                e[pos].diff = diff(i, j);;
            }
        }
        sort(e+1, e+1+pos);
        for (int i = 1; i <= pos; ++i) {
            a = find(e[i].x), b = find(e[i].y);
            if (a != b) {
                printf("%d %d\n", e[i].x, e[i].y);
                ++cnt;
                merge(a, b);
                ans += e[i].diff;
                if (cnt == N-1) {
                    break;
                }
            }
        }
        printf("The highest possible quality is 1/%d.\n", ans);
    }
    return 0;   
}