Hdu1232 畅通工程 【并查集】

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <cmath>
#include <queue>
using namespace std;
template <class T> void checkmin(T &t,T x) {if(x < t) t = x;}
template <class T> void checkmax(T &t,T x) {if(x > t) t = x;}
template <class T> void _checkmin(T &t,T x) {if(t==-1) t = x; if(x < t) t = x;}
template <class T> void _checkmax(T &t,T x) {if(t==-1) t = x; if(x > t) t = x;}
typedef pair <int,int> PII;
typedef pair <double,double> PDD;
typedef long long ll;
#define foreach(it,v) for(__typeof((v).begin()) it = (v).begin(); it != (v).end ; it ++)
const int N = 1111;
int f
, n , m;
bool vis
;
int find(int x) {
return x == f[x] ? x : f[x] = find(f[x]);
}
void Union(int x,int y) {
int a = find(x) , b = find(y);
f[a] = f[b] = f[x] = f[y] = min(a , b);
}
int main() {
while(~scanf("%d",&n) && n) {
scanf("%d",&m);
for(int i=1;i<=n;i++) f[i] = i , vis[i] = 0;
while(m--) {
int x , y;
scanf("%d%d",&x,&y);
Union(x ,  y);
}
int ans = -1;
for(int i=1;i<=n;i++) {
int x = find(i);
if(!vis[x]) {
vis[x] = 1;
ans ++;
}
}
printf("%d\n" , ans);
}
return 0;
}