int a[]={10,6,7,1,3,9,4,2};

int a[]={1,2,3};
int b[]={2,5,6};

while (begin1 <= end1 && begin2 <= end2)//begin指针指向两个有序数组的第一个元素.end为数组有效范围
  {
    if (a[begin1] < a[begin2])//谁小谁就先进tmp数组
    {
      tmp[i++] = a[begin1++];
    }
    else
    {
      tmp[i++] = a[begin2++];
    }
  }
  while (begin1 <= end1)//当其中一个数组走完后.将另外一个数组所有内容直接放进tmp数组
  {
    tmp[i++] = a[begin1++];
  }
  while (begin2 <= end2)//数组1先走完就将数组2剩下全部内容放进去
  {
    tmp[i++] = a[begin2++];
  }
  //将tmp数组的内容拷贝回a数组
  for (int j = left; j <= right; j++)
  {
    a[j] = tmp[j];
  }
}

//归并排序
void MergeSort(int* a, int n)
{
  int* tmp = (int*)malloc(sizeof(int) * n);//为临时数组tmp开辟空间
  if (tmp == NULL)
  {
    printf("动态开辟失败");
    exit(-1);
  }
  _MergeSort(a, 0, n - 1, tmp);//_MergeSort为递归函数.传参进行递归过程
  free(tmp);
  tmp = NULL;
}

//归并排序的子程序
void _MergeSort(int* a, int left, int right, int* tmp)
{
  if (left >= right)
  {
    return;
  }
  int mid = (left + right) / 2;
  _MergeSort(a, left, mid, tmp);//进了函数一直递归,直到数组元素为1个后开始归并排序
  _MergeSort(a, mid + 1, right, tmp);//先递归左边再递归右边
  int begin1 = left;
  int end1 = mid;
  int begin2 = mid + 1;
  int end2 = right;
  int i = left;
  while (begin1 <= end1 && begin2 <= end2)
  {
    if (a[begin1] < a[begin2])
    {
      tmp[i++] = a[begin1++];
    }
    else
    {
      tmp[i++] = a[begin2++];
    }
  }
  while (begin1 <= end1)
  {
    tmp[i++] = a[begin1++];
  }
  while (begin2 <= end2)
  {
    tmp[i++] = a[begin2++];
  }
  //将tmp数组的内容拷贝回a数组
  for (int j = left; j <= right; j++)
  {
    a[j] = tmp[j];
  }
}