快速排序及与随机快排间的性能比较

快排时间复杂度：nlogn

java代码1：对输入数组实现快排

import java.util.Scanner;

public class Temp {		
	public static void main(String[] args){
		Scanner s = new Scanner(System.in);
		int[] arr = new int[10];
		for(int i=0;i<arr.length;i++){
			arr[i] = s.nextInt();
		}
		printArr(arr);
		Temp t = new Temp();
		t.quickSort(arr, 0, arr.length-1);
		printArr(arr);
	}
	
	public void quickSort(int[] a,int left,int right){
		int i = left;
		if(left<right){
			for(int j = left;j<a.length;j++){
				if(a[j]<a[right]){
					swap(a,i,j);
					i = i+1;
				}
			}
			swap(a,i,right);
			quickSort(a,left,i-1);
			quickSort(a,i+1,right);
		}		
	}
	
	private void swap(int[] a,int i,int j){
		int temp;
		temp = a[i];
		a[i] = a[j];
		a[j] = temp;
	}
	
	public static void printArr(int[] a){
		for(int i=0;i<a.length;i++){
			System.out.print(a[i]+" ");
		}
		System.out.println();
	}
	
}

　　输出结果：

java代码2：对随机产生的10组包含一百万个数字（大小在0-1000之间）的数组进行快排和随机快排，并比较其排序时间。之后再对有序数组分别进行快排和随机快排，比较其性能。

package quickSort;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Random;

public class QuickSort {
	final static int arrlength = 1000000;
	static int arr[] = new int[arrlength];
	static int a1[],a2[];
	static SimpleDateFormat dfs = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");   
    static long between1;
	static long between2;
    
	public static void main(String[] args) throws ParseException{
		int num=0;
		QuickSort q = new QuickSort();
		QuickSort s= new QuickSort();
		for (int loop = 0;loop<10;loop++){
			int count = 0;
			Random random = new Random();
			while(count<arrlength){
				arr[count] = random.nextInt(1000);
				count++;
			}		
			a1=arr.clone();
			a2=arr.clone();
//			q.printArr(arr);
			java.util.Date begintime = dfs.parse(dfs.format(new Date()));
			q.quick(a1,0,a1.length-1);		
			java.util.Date middletime = dfs.parse(dfs.format(new Date()));
			s.random(a2,0,a2.length-1);
			java.util.Date endtime = dfs.parse(dfs.format(new Date()));
	        between1=middletime.getTime()-begintime.getTime();
	        between2=endtime.getTime()-middletime.getTime();
			System.out.print("快速排序耗时:"+between1+"ms ");
//			System.out.println();
//			q.printArr(a1);
	        System.out.println("随机快排耗时:"+between2+"ms ");
//			q.printArr(a2);
	        if(between1>between2)
	        	num++;
		}
		 System.out.println("随机快排更快的次数："+num);
		 
		 java.util.Date begintime = dfs.parse(dfs.format(new Date()));
		 q.quick(a2,0,a1.length-1);		
		 java.util.Date middletime = dfs.parse(dfs.format(new Date()));	
		 s.random(a2,0,a2.length-1);
		 java.util.Date endtime = dfs.parse(dfs.format(new Date()));
		 between1=middletime.getTime()-begintime.getTime();
		 between2=endtime.getTime()-middletime.getTime();
		 System.out.println("对有序序列排序： ");
		 System.out.println("快速排序耗时:"+between1+"ms ");
//		 q.printArr(a2);
		 System.out.println("随机快排耗时:"+between2+"ms ");
//		 s.printArr(a2);
	}
	
	public void quick(int[] a,int left,int right){
		if (left>=right){
			return;
		}
		int i = left;
		for(int j = left; j < right;j++){
			if(a[j]<a[right]){
				swap(a,i,j);
				i++;
			}
		}
		swap(a,i,right);
//		printArr(a);
		quick(a,left,i-1);
		quick(a,i+1,right);
	}
	
	private void swap(int[] a,int i,int j){
		int temp=a[i];
		a[i]=a[j];
		a[j]=temp;
	}
	
	public void random(int[] a,int left,int right){
		if(left >= right){
			return;
		}
		Random r = new Random();
		int index = (r.nextInt(right-left))+left;
		swap(a,index,right);
		quick(a,left,right);
	}
	
	private void printArr(int[] a){
	    for(int i=0;i<a.length;i++){
	        System.out.print(a[i] + " ");
	    }
	    System.out.println();
	}
}

　　输出结果：

 

一百万的数据量任然太小，随机快排的效果并不明显（效率并不是确定的），但对于有序数组，随机快排明显要更快。

 

转载于:https://www.cnblogs.com/tlyx/p/6810058.html