HDU_1232 畅通工程（并查集）

　　

#include <iostream>
#include <cstdio>
#include <cstring>
#pragma comment(linker,"/STACK:655360000");

using namespace std;

const int N = 1002;
int f[N], rank[N];

int find(int x)
{
    int k, r, j;
    r = x;
    while(r != f[r])
    {
        r = f[r];
    }
    k = x;
    while(k != r)
    {
        j = f[k];
        f[k] = r;
        k = j;
    }
    return r;
}

void union_set(int a, int b)
{
    int x = find(a);
    int y = find(b);
    if(x == y)    return;
    if(rank[x] > rank[y]) f[y] = x;
    else
    {
        f[x] = y;
        if(rank[x] == rank[y]) rank[y]++;
    }
}
int main()
{
    //freopen("data.in", "r", stdin);

    int n, m, i, a, b;
    while(scanf("%d", &n) != EOF)
    {
        if(n == 0)    break;
        scanf("%d", &m);
        if(m == 0)
        {
            printf("%d\n", n-1);
            continue;
        }
        for(i = 1;i <= n; i++)
        {
            f[i] = i;
            rank[i] = 0;
        }
        while(m--)
        {
            cin >> a >> b;
            union_set(a, b);
        }

        int cnt = 0;
        for(i = 1; i <=n; i++)
        { 
            if(find(i) == i)    //开始写成f[i] == i了，悲剧啊！！！
                cnt++;
        }
        printf("%d\n", cnt-1);
    }
    return 0;
}