归并排序-含对数器验证

package com.day1.sort;

import java.util.Arrays;

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

   public static void mergeSort(int[] arr, int l, int r) {
       if (l == r) {
           return;
       }
       int mid = l + ((r - l) >> 1);
       mergeSort(arr, l, mid);
       mergeSort(arr, mid + 1, r);
       merge(arr, l, mid, r);
   }

   public static void merge(int[] arr, int l, int m, int r) {
       int[] help = new int[r - l + 1];
       int i = 0;
       int p1 = l;
       int p2 = m + 1;
       while (p1 <= m && p2 <= r) {
           help[i++] = arr[p1] < arr[p2] ? arr[p1++] : arr[p2++];
       }
       while (p1 <= m) {
           help[i++] = arr[p1++];
       }
       while (p2 <= r) {
           help[i++] = arr[p2++];
       }
       for (i = 0; i < help.length; i++) {
           arr[l + i] = help[i];
       }
   }

   // for test
   public static void comparator(int[] arr) {
       Arrays.sort(arr);
   }

   // for test
   public static int[] generateRandomArray(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 isEqual(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 printArray(int[] arr) {
       if (arr == null) {
           return;
       }
       for (int i = 0; i < arr.length; i++) {
           System.out.print(arr[i] + " ");
       }
       System.out.println();
   }

   // for test
   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 = generateRandomArray(maxSize, maxValue);
           int[] arr2 = copyArray(arr1);
           mergeSort(arr1);
           comparator(arr2);
           if (!isEqual(arr1, arr2)) {
               succeed = false;
               printArray(arr1);
               printArray(arr2);
               break;
           }
       }
       System.out.println(succeed ? "Nice!" : "Fucking fucked!");

       int[] arr = generateRandomArray(maxSize, maxValue);
       printArray(arr);
       mergeSort(arr);
       printArray(arr);

   }

}