线性时间选择排序

快速排序的最佳状态是带有线性选择排序的  这样减少了时间复杂度提高了效率

package com.cb.suanfa;import java.util.Random;import java.util.Scanner;public class Main {public static void main(String[] args) {int [] arr = new int[9999999];Random random = new Random();Scanner scanner = new Scanner(System.in);System.out.println("产生多少随机数");int  n = scanner.nextInt();System.out.println("随机产生的数");for (int i = 0; i < n; i++) {arr[i] = random.nextInt(n*10);System.out.print(arr[i]+ "  ");if(i!=0 && i%200==0)System.out.println();}System.out.println();System.out.println("输出第几小的元素");int key = scanner.nextInt();int result = RandomizedSelect(arr,0,n-1,key);System.out.println("这个数为："+result);}private static int RandomizedSelect(int[] arr, int low, int high, int key) {if(low == high){return arr[low];}int i = RandomizedPartition(arr,low,high);int j = i-low+1;if(key<=j){return RandomizedSelect(arr,low,i,key);}else{return RandomizedSelect(arr, i+1, high, key-j);}}private static int RandomizedPartition(int[] arr, int low, int high) {Random rm = new Random();int i;  do{  i = rm.nextInt(high);  }while(i>low);  Swap(arr[i],arr[low]);   return Partition(arr,low,high);}//数据交换private static void Swap(int a,int b) {   int tmp=a;   a=b;   b=tmp; }  //快速排序private static int Partition(int a[],int low,int high) {    int i=low,j=high+1;   int x=a[low];  while(true)  {while(a[++i]<x&&i<high);while(a[--j]>x);if(i>=j) break;Swap(a[i],a[j]);   }   a[low]=a[j];  a[j]=x;   return j; } }