Algs4-2.1.25不需要交换的插入排序

2.1.25不需要交换的插入排序。在插入排序的实现中使较大元素右移一位只需访问一次数组(而不用使用exch())。使用SortCompare来评估这种做法的效果。
答：交换的成本较大，所以不交换方式性能提升10%

public class Insertion
{
    public static void sort(Comparable[] a)
    {
        int N=a.length;
        for (int i=0;i<N;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=0;i<a.length;i++)
            if(less(a[i],a[i-1])) return false;
        return true;
    }
   
     public static void main(String[] args)
    {
        int N=Integer.parseInt(args[0]);
        Double[] a=new Double[N];
        for(int i=0;i<N;i++)
            a[i]=StdRandom.uniform(0.0,N*1.0);
        //
        sort(a);
    }
}

public class Insertion3
{
    public static void sort(Comparable[] a)
    {
        int N=a.length;
        Comparable t;
        for (int i=0;i<N;i++)
        {
            t=a[i];
            int j;
            for(j=i;j>0 && less(t,a[j-1]);j--)
                a[j]=a[j-1];
            a[j]=t;
        }
    }
   
    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=0;i<a.length;i++)
            if(less(a[i],a[i-1])) return false;
        return true;
    }
   
     public static void main(String[] args)
    {
        int N=Integer.parseInt(args[0]);
        Double[] a=new Double[N];
        for(int i=0;i<N;i++)
            a[i]=StdRandom.uniform(0.0,N*1.0);
        //
        sort(a);
        //
        for (int i=0;i<N;i++)
           StdOut.printf("%4f  ",a[i]);
    }
}

public class SortCompare
{
    public static double time (String alg,Double[] a)
    {
        Stopwatch timer =new Stopwatch();
        if(alg.equals("Insertion")) Insertion.sort(a);
        //exercise2.1.24
        if(alg.equals("Insertion2")) Insertion2.sort(a);
        //exercise2.1.25
        if(alg.equals("Insertion3")) Insertion3.sort(a);
        //exercise2.1.26
        if(alg.equals("Insertion4")) Insertion3.sort(a);
        if(alg.equals("Selection")) Selection.sort(a);
        if(alg.equals("Shell")) Shell.sort(a);
       // if(alg.equals("Merge")) Merge.sort(a);
      //  if(alg.equals("Quick")) Quick.sort(a);
      //  if(alg.equals("Heap")) Heap.sort(a);
        return timer.elapsedTime();
    }
   
    public static double timeRandomInput(String alg,int N,int T)
    {
        double total =0.0;
        Double[] a=new Double[N];
        for (int t=0;t<T;t++)
        {
            for (int i=0;i<N;i++)
                a[i]=StdRandom.uniform();
            total+=time(alg,a);
        }
        return total;
    }//end timeRandomInput
   
    public static void main(String[] args)
    {
        String alg1=args[0];
        String alg2=args[1];
        int N=Integer.parseInt(args[2]);
        int T=Integer.parseInt(args[3]);
        double t1=timeRandomInput(alg1,N,T);
        double t2=timeRandomInput(alg2,N,T);
        StdOut.printf("For %d random Doubles\n %s is",N,alg1);
        StdOut.printf(" %.2f times faster than %s\n",t2/t1,alg2);
    }
   
}