博主檢視別人部落格以及Arrays.sort()總結出來的快排改進版

public class QucikSort {

	public static void main(String[] args) {
		//int a[]={9,8,6,1,2,5,4,8,3,7,1,2,0,15,12,11,13,18,9,7,5,6,4,12,17,20};
		int a[]={20,19,18,17,16,15,14,13,12,11,10,9,8,7,6,5,4,3,2,1,0};
		quickSort(a,0,a.length-1);
		output(a);

	}
	private static void output(int[] a) {
		for(int val:a)
			System.out.print(val+" ");
		
	}
	public static void quickSort(int[] a,int left,int right){
		if(a.length==0||left<0||right<0||left>right)
			return;
		int len=right-left+1;
		
		if(len<7){
			for(int i=left;i<=right;i++){
				int temp=a[i]; 
				int j=i-1;
				for(;j>=left&&a[j]>=temp;j--)
					a[j+1]=a[j];
				a[j+1]=temp;
			}
			return ;
		}
		int l=left;
		int m=left+len>>1;
		int n=left+len-1;
		int s=len/8;
		if(len>40){
			
			l = med3(a, l, l + s, l + 2 * s); // 取樣左端點3個數並得出中數
            m = med3(a, m - s, m, m + s); // 取樣中點3個數並得出中數
            n = med3(a, n - 2 * s, n - s, n); // 取樣右端點3個數並得出中數
		}
		m = med3(a, l, m, n);
		swap(a,left,m);
		
		int x=a[left];
		int i=left;
		int j=right;
		while(i<j){
			
			while(a[j]>=x) j--;
			if(i<j) a[i++]=a[j];
			while(a[i]<x)	i++;
			if(i<j)	a[j--]=a[i];
		}
		a[i]=x;
		quickSort(a,left,i-1);
		quickSort(a,i+1,right);
	}
	
	private static void swap(int[] a, int x, int y) {
		int temp=a[x];
		a[x]=a[y];
		a[y]=temp;
		
	}
	private static int med3(int x[], int a, int b, int c) {
        return x[a] < x[b] ? (x[b] < x[c] ? b : x[a] < x[c] ? c : a)
                : x[b] > x[c] ? b : x[a] > x[c] ? c : a;
    }
}