C ++删除和压缩二维动态数组中的偶数行

Question

我需要帮助

这个程序必须做的：

•删除所有偶数行

•将剩余的行压缩到二维数组的顶部

https://gyazo.com/64954d5a5ace39e7bb4264f2e2a9ecdf

代码：

int main(int argc, char ** argv){
   int ** array2d;

   int size = 10;
   array2d = new int *[size];
   cout << "***** Before Compaction ******" << endl;
   for (int i = 0; i < size; i++) {
      array2d[i] = new int[size];
      cout << "ROW " <<i << ":";
      for (int j = 0; j < size; j++) {
         array2d[i][j] = i;
         cout << " "<< array2d[i][j];
      }
      cout << endl;
   }

   //NEED HELP WITH THIS PART DOWN HERE


   for (int i = 0; i < size; i++) {
      if (i % 2 == 0) { // delete the even rows
         delete[] array2d[i];
         array2d[i] = NULL;
      }
      // for each row in the first half, redirect the pointer
      // to the next odd row
      if(i<size/2){
         array2d[i] = array2d[2 * i + 1];
         array2d[2 * i + 1] = NULL;

      }

      cout << endl;
   }
   return 0;
}

Answer 1

  if (i % 2 == 0) { // delete the even rows
     delete[] array2d[i];
     array2d[i] = NULL;
  }

i == 0 对应第一行。我认为您可能希望将其更改为：

  if ((i+1) % 2 == 0) { // delete the even rows
     delete[] array2d[i];
     array2d[i] = NULL;
  }

然后，

     array2d[i] = array2d[2 * i + 1];
     array2d[2 * i + 1] = NULL;

需要：

     array2d[i] = array2d[2 * i];
     array2d[2 * i] = NULL;

更新

你所拥有的和我建议的问题是你正在泄漏内存。使用时：

     array2d[i] = array2d[2 * i];

分配给array2d[i] 的内存丢失。您无法释放该内存。您可能希望交换指针值以释放所有内存。

     int* temp = array2d[i];
     array2d[i] = array2d[2 * i];
     array2d[2 * i] = temp;