学步园

题目链接：

http://acm.hdu.edu.cn/showproblem.php?pid=1232

/*
典型的并查集习题，思路比较简单，只需要找出有几棵树就可以了
*/
#include <iostream>
using namespace std;

const int MAX = 1001;
int father[MAX];
int rank[MAX];

void Make_Set(const int n) {
 for (int i = 1; i <= n ; i++) {
  father[i] = i;
  rank[i] = 0;
 }
}
int Find_Set(const int x) {
 if (father[x] != x)
  father[x] = Find_Set(father[x]);
 return father[x];
}
void Union (int x, int y) {
 x = Find_Set(x);
 y = Find_Set(y);
 if (x == y) return ;
 if (rank[x] > rank[y]) father[y] = x;
 else if (rank[x] < rank[y]) father[x] = y;
 else {
  rank[y]++; father[x] = y;
 }
}
int main ()
{
 int n, m;
 int a, b;
 while (cin >> n && n) {
  cin >> m;
  Make_Set(n);
  while (m--) {
   cin >> a >> b;
   Union(a, b);
  }
  int count = -1;
  for (int i = 1; i <= n; i++)
   if (father[i] == i)
    count ++;
  cout << count << endl;
 }
}