java中归并排序和Master公式详解

  public static void MergeSort(int[] arr,int l , int r) {
        if (l == r || r < 0){
            return;
        }
        int middle = l+(r-l)/2; //取中值，可以防止达到Integer.MaxValue 溢出
        MergeSort(arr,l,middle);
        MergeSort(arr,middle+1,r);
        sort(arr,l,middle,r);
    }
    /**
     *
     * @param arr 等待排序的数组
     * @param l 左数组第一个指针
     * @param middle 分割左右数组
     * @param r 右数组最后一个指针
     */
    private static void sort(int[] arr, int l, int middle, int r) {
        int[] temp = new int[arr.length];
        System.arraycopy(arr, 0, temp, 0, arr.length);
        int right_first = middle+1;
        int tempIndex = l;
        while (l <= middle && right_first <= r){
            if (temp[tempIndex] < temp[right_first]){
                arr[l++] = temp[tempIndex++];
            }else {
                arr[l++] = temp[right_first++];
            }
        }
        while (tempIndex <= middle){
            arr[l++] = temp[tempIndex++];
        }
        while (right_first <= r ){
            arr[l++] = temp[right_first++];
        }

    }

   //生成1-100内随机数组
   public static int[] getParamArrays(){
        int[] result = new int[(int) (Math.random() * 100)];
        //随机生成数
        for (int i = 0; i < result.length; i++) {
            result[i] = (int) (Math.random() * 100);
        }
        return result;
    }
    public static void main(String[] args){
        for (int i = 0; i < 1000000; i++) {
            int[] nums = getParamArrays();
            int[] temp = nums;
            MergeSort(nums,0,nums.length-1);
            Arrays.sort(temp);
            //通过自定义比较次数，对随机数组进行排序验证正确性
            if (!nums.equals(temp)){
                System.out.println("wrong");
            }
        }
        System.out.println("end");
    }