并查集：

#include 
     
      using namespace std;const int cityNum = 1000 ;int city[cityNum];int N,M;int total;void init(){     for(int i=1;i<=N;i++){        city[i] = i;    }}int findSet(int x){     int tmp = x;    do{        tmp = city[tmp];    }while(tmp != city[tmp]);    city[x] = tmp;    return tmp;}void unionSet(int x,int y){
   //Y->X    int xP = findSet(x);    int yP = findSet(y);    if(xP != yP){        total--;        city[yP] = xP;        city[y] = xP;     }}int main(){    int city1,city2;    while(scanf("%d %d",&N,&M) && N){        total = N-1;        init();        for(int i=0;i