DSA · Theory

Delete Mid of a Stack

Theory

809/810

Delete Mid of a Stack sits in a tiny editor. Dev’s job is undo typing. Write that first.

Do Delete Mid of a Stack once by hand. push / pop LIFO. Change one input. Say the new result out loud.

Without Delete Mid of a Stack, a tiny editor gets messy and undo typing is hard to trust.

Dev ships Delete Mid of a Stack in a tiny editor. That is the use case worth saying.

Delete Mid of a Stack trap — pop on empty. Dev loses marks for that every viva.

After Delete Mid of a Stack, Dev should still remember pop on empty.

Viva for Delete Mid of a Stack — what it is → push / pop LIFO → the mistake (pop on empty).

Diagram

    | 3 |  ← top (pop)
    | 2 |
    | 1 |
    LIFO

Exam tip

For Delete Mid of a Stack: definition + a tiny editor + one failure.

stack = []
stack.append(10)   # push
stack.append(20)
print(stack.pop()) # 20
print(stack[-1])   # peek → 10

Delete Mid of a Stack — stack is LIFO: push/pop from the same end.