Algs4-1.5-quick-union

public class UF
{
    private int[] id;
    private int count;
    public UF(int N)
    {
        count=N;
        id=new int[N];
        for (int i=0;i<N;i++)
            id[i]=i;
    }
   
     public int count()
     {return count;}
    
      boolean connected(int p,int q)
      {return find(p)==find(q);}
      /*quick-find
       public int find(int p)
       {return id[p];}
      
       public  void union(int p,int q)
       {
          int pID=find(p);
          int qID=find(q);
          if (pID==qID) return;
          for (int i=0;i<id.length;i++)
              if(id[i]==pID) id[i]=qID;
          count--;
       }
       */
      public int find(int p)
      {
          while(p!=id[p]) p=id[p];
          return p;
      }
     
      public void union(int p,int q)
      {
          int pRoot=find(p);
          int qRoot=find(q);
          if(pRoot==qRoot) return;
          id[pRoot]=qRoot;
          count--;
      }
      
       public static void main(String[] qrgs)
       {
           int N=StdIn.readInt();
           UF uf=new UF(N);
           while (!StdIn.isEmpty())
           {
               int p=StdIn.readInt();
               int q=StdIn.readInt();
               if(uf.connected(p,q)) continue;
               uf.union(p,q);
               StdOut.println(p+ " " +q);
            }//end while
        }//end main
}//end class