算法(第四版)学习笔记之java实现希尔排序

希尔排序思想：使数组中随意间隔为h的元素都是有序的。

希尔排序是插入排序的优化。先对数组局部进行排序，最后再使用插入排序将部分有序的数组排序。

代码例如以下：

/**
 * 
 * @author seabear
 *
 */

public class ShellSort {
	public static void sort(Comparable[] a)
	{
		int N = a.length;
		int h = 1;
		while(h < N/2)
		{
			h = 4 * 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)
				{
					int n = j - h;
					System.out.println(j + ":" + a[j] + "," + n + ":" + a[j-h]);
					exch(a,j,j-h);
					show(a);
				}
			}
			h = h / 4;
		}
	}
	
	public static boolean less(Comparable v,Comparable w)
	{
		return v.compareTo(w) < 0;
	}
	
	public static void exch(Comparable[] a,int i,int j)
	{
		Comparable temp = a[i];
		a[i] = a[j];
		a[j] = temp;
	}
	
	public static boolean isSort(Comparable[] a)
	{
		for(int i = 1; i < a.length; i++)
		{
			if(less(a[i],a[i-1]))
			{
				return false;
			}
		}
		return true;
	}
	
	public static void show(Comparable[] a)
	{
		for(int i = 0; i < a.length; i++)
		{
			System.out.print(a[i] + " ");
		}
		System.out.println();
	}
	
	public static void main(String[] args)
	{
		Integer[] a = new Integer[10];
		for(int i = 0; i < 10; i++)
		{
			a[i] = (int)(Math.random() * 10 + 1);
			System.out.print(a[i] + " ");
		}
		System.out.println();
		sort(a);
		show(a);
	}
}