2.1.12

question:

Instrument shellsort to print the number of compares divided by rhe array size for each increment. Write a test client that tests the hypothesis that this number is a small constant, by sorting arrays of random Double values, using array size that are increasing powers of 10, starting at 100.

answer:

//我没有用10的幂，这样结果比较清楚

//我自认为自己是对的，要是有错误的话还请指出

import edu.princeton.cs.algs4.*;

public class Shell
{
    public static int sort(Comparable[] a)//返回比较次数
    {
        int count = 0;//存比较次数
        int N = a.length;
        int h = 1;
        while(h < N/3) h = 3*h + 1;
        while(h>=1)
        {
            for(int i = h; i < N; i++)
            {
                //网上有答案在这里加count++,但less才是比较啊,这里明显不是比较次数吧
                for(int j = i; j >= h; j-=h)//比较后也不一定不交换,所以把循环拆开好看比较次数
                {
                    count++;
                    if(less(a[j],a[j-h]))
                    {
                        exch(a,j,j-h);
                    }
                    else
                        break;
                }
            }
            h = h/3;
        }
        return count;
    }
    
    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 size = 100;
        int i = 2;
        while(i <= 40)
        {
            Double[] a = new Double[size + i * 100];
            for(int j = 0; j < size + i *100; j++)
                a[j] = StdRandom.uniform();
            int count = sort(a);
            double rate = (double)(size+i*100) / count;
            StdOut.println(rate);
            i++;
        }
    }
}