Reverse a stack using recursion | GeeksforGeeks

You are not allowed to use loop constructs like while, for..etc, and you can only use the following ADT functions on Stack S:
isEmpty(S)
push(S)
pop(S)

The idea of the solution is to hold all values in Function Call Stack until the stack becomes empty. When the stack becomes empty, insert all held items one by one at the bottom of the stack.

void insertAtBottom(struct sNode** top_ref, int item)

{

   int temp; 

   if(isEmpty(*top_ref))

   { 

       push(top_ref, item);

   }

   else

   {

     /* Hold all items in Function Call Stack until we reach end of

       the stack. When the stack becomes empty, the isEmpty(*top_ref)

       becomes true, the above if part is executed and the item is

       inserted at the bottom */

     temp = pop(top_ref);

     insertAtBottom(top_ref, item);

     /* Once the item is inserted at the bottom, push all the

          items held in Function Call Stack */

     push(top_ref, temp);

   }            

} 

void reverse(struct sNode** top_ref)

{

  int temp;  

  if(!isEmpty(*top_ref))

  {

    /* Hold all items in Function Call Stack until we reach end of

     the stack */

    temp = pop(top_ref);                       

    reverse(top_ref);

    /* Insert all the items (held in Function Call Stack) one by one

       from the bottom to top. Every item is inserted at the bottom */

    insertAtBottom(top_ref, temp);

  }     

}

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