排序-快速排序-优化-基准值选择待排序数组的三个等距取样的中位数

package xwq.sort;import xwq.util.In;import xwq.util.StdOut;/** * 使用三取样partition优化QuickSort */public class QuickSortMid {    public static void sort(int a[]) {        partition(a,0,a.length-1);    }    //划分    private static void partition(int a[],int low,int high) {        if(low >= high)            return;        int N = high - low + 1;        //抽取三个等距离的数，选择其中中位数作为基准值        if(N > 40) {            int len = N/8;            int mid = low+N/2;            int m1 = median3(a,low,low+len,low+len+len);             int m2 = median3(a,mid-len,mid,mid+len);            int m3 = median3(a,high-len-len,high-len,high);            int m = median3(a,m1,m2,m3);        }        else if(N >=3) {            int m = median3(a,low,low+N/2,high);            swap(a,low,m);        }        int pivot = a[low];        int l = low,h = high;        while( l < h) {            while(l<h && a[h]>=pivot) h--;            if(l<h) swap(a,l++,h);            while(l<h && a[l]<=pivot) l++;            if(l<h) swap(a,l,h--);        }        a[l] = pivot;        partition(a,low,l-1);        partition(a,l+1,high);    }    /*     * 返回3个数的中位数     */    private static int median3(int a[],int low,int mid,int high) {        if(a[low] > a[mid] && a[low] < a[high])            return low;        if(a[low] > a[mid] && a[mid] < a[high])            return mid;        return high;    }    private static void swap(int a[],int i,int j) {        int t = a[i]; a[i] = a[j]; a[j] = t;    }    public static void print(int a[]) {        for (int i = 0; i < a.length; i++)            StdOut.print(a[i] + " ");        StdOut.println();    }    // 测试函数    public static void main(String[] args) {        int[] a = In.readInts(args[0]);        sort(a);        print(a);    }}