C :

#include <stdio.h>

int total;
int pre[1001];

void init(int n){
	int i;
	for(i=1;i<=n;++i){
		pre[i] = i;
	}
}

int root(int x){

	if(x!=pre[x]){
		pre[x] = root(pre[x]);
	}
	return pre[x];
}

void merge(int a,int b){

	int x = root(a);
	int y = root(b);
	if(x!=y){
		pre[x]=y;
		--total;
	}
}

int main(){
	int N,M,i,st,end;
	while(scanf("%d",&N) && N){
		
		scanf("%d",&M);

		init(N);

		total = N-1;

		for(i=0;i<M;++i){
			scanf("%d %d",&st,&end);
			merge(st,end);
		}
		printf("%d\n",total);
	}
	return 0;
}

C++ :

#include<stdio.h>

int p[1000];

int Find(int i)
{
	return i==p[i]?i:p[i]=Find(p[i]);
}

void Union(int a,int b)
{
	p[a]=b;
}

int main()
{
	int n,m,i,s,e,a,b,ans;
	while(scanf("%d",&n)!=EOF,n)
	{
		scanf("%d",&m);
		for(i=1;i<=n;i++)
			p[i]=i;
		while(m--)
		{
			scanf("%d%d",&s,&e);
			a=Find(s);
			b=Find(e);
			if(a!=b)
				p[a]=b;
		}
		for(ans=0,i=1;i<=n;i++)
			if(p[i]==i)
				ans++;
		printf("%d\n",ans-1);
	}
	return 0;
}

Pascal :

var
  father:array[1..1000]of longint;
	i,j,n,q,ans,x,y:longint;
function search(x:longint):longint;
begin
  if father[x]<>x then father[x]:=search(father[x]);
  exit(father[x]);
end;
procedure judge(x,y:longint);
var a,b:longint;
begin
  a:=search(x); b:=search(y);
  if a<>b then father[b]:=a;
end;
begin
  read(n);
  while n<>0 do begin
      read(q);
	for i:=1 to n do father[i]:=i;
	for i:=1 to q do begin
	  read(x,y);
		judge(x,y);
	end;
	ans:=0;
	for i:=1 to n do
	  if father[i]=i then inc(ans);
	writeln(ans-1);
        read(n);
        end;
end.

Java :

import java.util.Scanner;
public class Main{
	static int m,n;
	static int ans=0;
	static int a[]=new int[1000010];
	static int[]pre=new int[1000010];
	static void init() {
		for(int i=0;i<=m;i++) {
			pre[i]=i;
		}
	}
	static int find(int x) {
		if(pre[x]==x) return x;
		return pre[x]=find(pre[x]);
	}
	static void join(int x,int y) {
		int fx=find(x);
		int fy=find(y);
		if(fx!=fy) {
			pre[fx]=fy;
		}
	}
	static boolean judge(int x,int y) {
		return find(x)==find(y);
	}
	public static void main(String[]args) {
		Scanner sc=new Scanner(System.in);
		while(true) {
			for(int i=0;i<=m;i++) a[i]=0;
		m=sc.nextInt();
		if(m==0)break;
		init();
		n=sc.nextInt();
		for(int i=0;i<n;i++) {
			int u=sc.nextInt();
			int v=sc.nextInt();
			join(u, v);
		}for(int i=1;i<=m;i++) {
			a[find(i)]=-1;
			if(a[i]!=-1) ans++;
		}System.out.println(m-ans-1);
		ans=0;
	}
	}
}