2.3.5

question:

Give a code fragment that sorts an array that is known to consist of items having just two distinct keys.

answer:

//就是三取样切分的简化版

import edu.princeton.cs.algs4.*;

public class Quick2way
{
    private static void exch(Comparable[] a, int i, int j)
    {
        Comparable t = a[i];
        a[i] = a[j];
        a[j] = t;
    }

    private static boolean less(Comparable v, Comparable w)
    {
        return v.compareTo(w) < 0;
    }

    private static void sort(Comparable[] a, int lo, int hi)
    {
        Comparable v = a[lo];
        int i = lo + 1, gt = hi;
        while(i < gt)//一遍循环就行了
        {
            if(less(v,a[i]))
                exch(a,i,gt--);
            else
                i++;
        }
    }

    public static void show(Comparable[] a)
    {
        for(Comparable c : a)
            StdOut.print(c + " ");
        StdOut.println();
    }

    public static void main(String[] args)
    {
        Integer[] a = {1,1,1,2,1,1,2,2,1,1,2,2,2,1,1,1};
        sort(a, 0, a.length-1);
        show(a);
    }
}

原文地址：https://www.cnblogs.com/w-j-c/p/9129454.html