计数排序_数组与集合时间比较

计数排序_数组与集合时间比较

Integer []与ArrayList比较

package com.m.demo;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class Test1 {
	public static void main(String[] args) {
		List<Integer> list = new ArrayList<Integer>();
		Random random = new Random();
		Test2 test2 = new Test2();
		int n = 15000;
		Integer [] arr = new Integer [n];
		for (int i = 0; i < n; i++) {
			//10~20
			list.add(random.nextInt(11)+10);
			arr[i] = list.get(i);
		}
		
		
		long startTime = System.currentTimeMillis();
		test2.countSort(list);
		long endTime = System.currentTimeMillis();
		System.out.println("ArrayList:"+(endTime-startTime));
		
		startTime = System.currentTimeMillis();
		sort(arr);
		endTime = System.currentTimeMillis();
		System.out.println("数组:"+(endTime-startTime));
		/*
		    List:9
			数组:4
		 */
		
	}
	
    public static int[] sort(Integer[] is) {
        //1.寻找最大值，来寻找新开辟空间的上限
        int max = is[0];
        for (int i = 1; i < is.length; i++) {
            if (is[i] > max) {
                max = is[i];
            }
        }
        //2.根据最大值创建空间
        int[] count = new int[max + 1];
        //3.遍历数组，统计各个元素的个数
        for (int i = 0; i < is.length; i++) {
            count[is[i]]++;//找到对应的位置，计数+1
        }
        //4.遍历统计后的数据，输出结果
        int index = 0;
        int[] sorted = new int[is.length];
        for (int i = 0; i < count.length; i++) {
            //每个计数要往排序后的数组放若干次
            for (int j = 0; j < count[i]; j++) {
                sorted[index++] = i;
            }
        }
        return sorted;
    }
}

ArrayList:9
数组:4

LinkedList与Integer []比较

LinkedList:267
数组:4

List计数代码

package com.m.demo;

import java.util.List;

public class Test2 {
	
	public void countSort(List<Integer> list){
		//1、找最大值
		Integer max = 0;
		for(Integer i:list) {
			if(max<i) {
				max = i;
			}
		}
		//2、创建排序数组
		int count [] = new int [max+1];
		for (int i = 0; i < list.size(); i++) {
			int j = list.get(i);
			count[j]++;
		}
		
		list.clear();
		for (int i = 0; i < count.length; i++) {
			for (int j = 0; j < count[i]; j++) {
				list.add(i);
			}
		}
	}
	/**
	 * 交换list中的a与b
	 * @param list
	 * @param a
	 * @param b
	 */
	private void swap(List<Integer> list,int a,int b) {
		int temp = list.get(a);
		list.set(a, list.get(b));
		list.set(b, temp);
	}
}