hdu1232 畅通工程 基础并查集

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

#define MAXN 1005
int n, m;
int fa[MAXN];    //父节点
int mark[MAXN];

void init()
{
    for (int i = 0; i <= n; i++)
    {
        fa[i] = i;
        mark[i] = 0;
    }
}

int find(int x)
{
    if (x == fa[x])
        return x;
    else
        return fa[x] = find(fa[x]);
}

void set_union(int x, int y)
{
    int x1 = find(x);
    int y1 = find(y);

    if (x1 == y1)
        return;
    if (mark[x1] < mark[y1])
    {
        fa[x1] = y1;
    }
    else
        fa[y1] = x1;
    if (mark[x1] == mark[y1])
        mark[x1]++;
}

int main()
{
    while (~scanf("%d",&n))
    {
        if (n == 0)
            break;
        scanf("%d", &m);
        init();
        for (int i = 0; i < m; i++)
        {
            int a, b;
            scanf("%d %d", &a, &b);
            set_union(a, b);
        }

        int ans = 0;
        for (int i = 1; i <= n; i++)
        {
            if (find(i) == i)
                ans++;
        }
        printf("%d
", ans - 1);
    }
    //system("pause");
    return 0;
}