快速排序

时间复杂度O(nlogn)

import java.util.Arrays;

public class Code_04_QuickSort {
    public static void quickSort(int[] arr) {
        if (arr == null || arr.length < 2) {
            return;
        }
        quickSort(arr, 0, arr.length - 1);
    }

    public static void quickSort(int[] arr, int l, int r) {
        if (l < r) {
            swap(arr, l + (int) (Math.random() * (r - l + 1)), r);  //随机快死排序
            int[] p = partition(arr, l, r);
            quickSort(arr, l, p[0] - 1);
            quickSort(arr, p[1] + 1, r);
        }
    }

    public static int[] partition(int[] arr, int l, int r) {
        int less = l - 1;
        int more = r;
        while (l < more) {
            if (arr[l] < arr[r]) {
                swap(arr, ++less, l++);
            } else if (arr[l] > arr[r]) {
                swap(arr, --more, l);
            } else {
                l++;
            }
        }
        swap(arr, more, r);
        return new int[] { less + 1, more };
    }

    private static void swap(int[] arr, int i, int r) {
        int temp=arr[i];
        arr[i]=arr[r];
        arr[r]=temp;
    }
    //for test
    public static int []generaeteRandomArray(int maxSize,int maxValue){
        int []arr=new int[(int)((maxSize+1)*Math.random())];
        for (int i = 0; i < arr.length; i++) {
            arr[i]=(int)((maxValue+1)*Math.random())-(int)((maxValue)*Math.random());

        }
        return arr;
    }
    //for test
    public static int []copyArray(int []arr){
        if (arr==null){
            return null;

        }
        int []res=new int[arr.length];
        for (int i = 0; i < arr.length; i++) {
            res[i]=arr[i];

        }
        return res;
    }
    //for test
    public static boolean isEquals(int []arr1,int []arr2){
        if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {

            return false;
        }
        if(arr1==null&&arr2==null){
            return true;
        }
        if(arr1.length!=arr2.length){
            return false;
        }
        for (int i = 0; i < arr1.length; i++) {
            if(arr1[i]!=arr2[i]){
                return false;
            }
        }
        return true;
    }
    //for test
    public static void comparator(int []arr){
        Arrays.sort(arr);
    }

    //for test
    public static void printArray(int []array){
        if (array==null){
            return;
        }
        for (int i = 0; i < array.length; i++) {
            System.out.print(array[i]);

        }
        System.out.println();

    }

    public static void main(String[] args) {
        int testTime=500000;
        int maxSize=100;
        int maxValue=100;
        boolean succeed=true;
        for (int i = 0; i < testTime; i++) {
            int []arr1=generaeteRandomArray(maxSize,maxValue);
            int []arr2=copyArray(arr1);
            quickSort(arr1);
            comparator(arr2);
            if (!isEquals(arr1,arr2)){
                succeed=false;
                printArray(arr1);
                printArray(arr2);
                break;
            }

        }
        System.out.println(succeed? "Nice !": "Fucking fucked!");
        int []arr=generaeteRandomArray(maxSize,maxValue);
        printArray(arr);
        quickSort(arr);
        printArray(arr);
    }

}