并查集练习

#define _CRT_SECURE_NO_DEPRECATE
#include<stdio.h>
#define MAX 1100
int par[MAX], n;
int find(int x){
    if (par[x] == x){
        return x;
    }
    return par[x] = find(par[x]);
}
void united(int x, int y){
    int a = find(x), b = find(y);
    if (a != b){ par[a] = b; }
}
int main()
{
    int m, a, b, i, res;
    while (scanf("%d", &n)!=-1, n){
        scanf("%d", &m);
        for (i = 1; i <= n; i++)par[i] = i;
        for (i = 0; i < m; i++){
            scanf("%d %d", &a, &b);
            united(a, b);
        }
        res = 0;
        for (i = 1; i <= n; i++){
            if (par[i] == i){
                res = res + 1;
            }
        }
        printf("%d\n", res - 1);
    }
    return 0;
}