希尔排序

希尔排序的关键思想是使序列中任意间隔h的元素都是有序的，其中h是一个递增序列，使得该递增序列（如1/2 (3^k-1))递减（从N / 3开始递减到1），当h为1时，整个序列就是有序的了。简易实现及测试用例如下：

import java.util.logging.Handler;


public class Shell {

    private static void exch(Comparable[] a, int i , int j){
        Comparable tmp = a[i];
        a[i] = a[j];
        a[j] = tmp;
    }
    
    private static boolean less(Comparable a, Comparable b)
    {
        return (a.compareTo(b) < 0);
    }
    
    private static void show(Comparable[] a)
    {
        int N = a.length;
        for(int i = 0; i < N; i++)
        {
            System.out.print(a[i] + " ");
        }
        System.out.println();
    }
    
    public static boolean isSorted(Comparable[] a)
    {
        int N = a.length;
        for(int i = 1; i < N; i++)
        {
            if(less(a[i], a[i - 1])) return false;
        }
        return true;
    }
    
    public static void sort(Comparable[] a)
    {
        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++)
            {
                for(int j = i; j >= h && less(a[j], a[j - h]); j -= h)
                    exch(a, j, j - h);
            }
            h = h / 3;
        }
    }

    public static void main(String[] args) {
        String[] a = StdIn.readAllStrings();
        Selection.sort(a);
        show(a);
    }
}