Delete Middle of a Stack

Given a stack s, remove the middle element of it without using any additional data structure.

Input: s = [10, 20, 30, 40, 50]
Output: s = [10, 20, 40, 50]
Explanation: After deleting the mid which is 30, stack will look like [10, 20, 40, 50].

Input: s = [1, 2, 3, 4]
Output: s = [1, 3, 4]
Explanation: The stack has 10 elements (even), there are two mid elements 2 and 3, we delete the first of the two.

Note : The output printed by the following codes is reverse of the order as we pop the top elements one by one and print.

Using Vector - O(n) Time and O(n) Space

• Create a vector to store stack elements.
• Pop all elements from the stack and store them in the vector.
• Identify the middle element index: n/2 for even n, ceil(n/2) for odd n (0-based indexing).
• Skip the middle element and push the remaining elements back to the stack in reverse order.

50 40 20 10 

Using Recursion - O(n) Time and O(n) Space

• Store the stack size (n) and initialize a counter (current) to track popped elements.
• Recursively, Pop an element and increment current and If current == n/2, pop the middle element and stop recursion. Otherwise, continue recursion.
• Push back the popped element after the recursive call.

50 40 20 10 

Using Temporary Stack - O(n) Time and O(n) Space

• Initialize a temporary stack and a counter (count).
• While count < n/2, pop elements from the original stack and push to the temporary stack.
• Pop the middle element from the original stack.
• While the temporary stack is not empty, pop elements from it and push to the original stack.

50 40 20 10