Algs4-2.3.27忽略小数组

Posted 2021-01-15 longjin2018

2.3.27忽略小数组。用实验对比以下处理小数组的方法和练习2.3.25的处理方法的效果：在快速排序中直接忽略小数组，仅在快速排序结束后运行一次插入排序。注意：可以通过这些实验估计出电脑的缓存大小，因为当数组大小超出缓存时这种方法的性能可能会下降。
public class E2d3d27
{
    public static void sort1(Comparable[] a,int M)
    {
      //StdRandom.shuffle(a);
      sort1(a,0,a.length-1,M);
    }
   
    private static void sort1(Comparable[] a,int lo,int hi,int M)
    {
        //数组少于等于M个元素时使用插入排序
        if (hi-lo+1<M)
        {
            InsertSort(a,lo,hi);
            return;
        }
        int j=partition(a,lo,hi);
        sort1(a,lo,j-1,M);
        sort1(a,j+1,hi,M);
    }
 
    public static void sort2(Comparable[] a,int M)
    {
      //StdRandom.shuffle(a);
      sort2(a,0,a.length-1,M);
    }
   
    private static void sort2(Comparable[] a,int lo,int hi,int M)
    {
        //数组少于等于M个元素时使用插入排序
        if (hi-lo+1<M) return;
        int j=partition(a,lo,hi);
        sort2(a,lo,j-1,M);
        sort2(a,j+1,hi,M);
    }
   
    private static int partition(Comparable[] a,int lo,int hi)
    {
        int i=lo,j=hi+1;
        Comparable v=a[lo];
        while(true)
        {
            while(less(a[++i],v)) if(i==hi) break;
            while(less(v,a[--j])) if(j==lo) break;
          
            if(i>=j) break;
            exch(a,i,j);
        }
        exch(a,lo,j);
        return j;
    }
   

     private static void InsertSort(Comparable[] a,int lo,int hi)
    {
        for (int i=lo+1;i<hi+1;i++)
        {
            for (int j=i;j>0 && less(a[j],a[j-1]);j--)
                exch(a,j,j-1);
          }
    }
       
    private static boolean less(Comparable v,Comparable w)
    { return v.compareTo(w)<0;}
   
    private static void exch(Comparable[] a,int i,int j)
    {
        Comparable  t=a[i];
        a[i]=a[j];
        a[j]=t;
    }
   
    private static void show(Comparable[] a)
    {
        for (int i=0;i<a.length;i++)
            StdOut.print(a[i]+" ");
        StdOut.println();
    }
   
    public static boolean isSorted(Comparable[] a)
    {
        for (int i=1;i<a.length;i++)
            if(less(a[i],a[i-1])) return false;
        return true;
    }
 
 
    public static void main(String[] args)
    {
        int Nlen[]={100000,500000,1000000,5000000};
        for(int Ni=0;Ni<Nlen.length;Ni++)
        {
          int N=Nlen[Ni];
          //生成一个长度为N的数组a
          Double[] a=new Double[N];
          for(int i=0;i<N;i++)
            a[i]=StdRandom.random(); 
          //
          int M=11;
          //生成数组a的两个副本aClone1、aClone1
          Double[] aClone1=new Double[N];
          for (int i=0;i<a.length;i++)
              aClone1[i]=a[i];
         
          Double[] aClone2=new Double[N];
          for (int i=0;i<a.length;i++)
             aClone2[i]=a[i];
          //数组长度为N,小于等于M时切换到插入排序的快速排序
          Stopwatch timer1=new Stopwatch();
          sort1(aClone1,M);
          double t1=timer1.elapsedTime();
          //数组长度为N,小于等于M忽略小数组的快速排序
          Stopwatch timer2=new Stopwatch();
          sort2(aClone2,M);
          InsertSort(aClone2,0,aClone2.length-1);
          double t2=timer2.elapsedTime();
         
          StdOut.printf("N=%d,T1=%f,T2=%f,t1-t2=%f ",N,t1,t2,t1-t2);
        }//end for Ni
      
    }//end main
}//end class