DSA · Theory

How to create a mergeable stack

Theory

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If you can teach How to create a mergeable stack using undo typing, you know it. If you only know the heading, you don’t.

Do How to create a mergeable stack once by hand. push / pop LIFO. Change one input. Say the new result out loud.

How to create a mergeable stack exists so Zara can keep undo typing correct in a tiny editor.

Zara ships How to create a mergeable stack in a tiny editor. That is the use case worth saying.

How to create a mergeable stack trap — pop on empty. Zara loses marks for that every viva.

How to create a mergeable stack is not a lonely heading. Zara ties it to undo typing.

Viva for How to create a mergeable stack: what it is → push / pop LIFO → the mistake (pop on empty).

Diagram

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

Exam tip

Say How to create a mergeable stack in one breath, then push / pop LIFO, then pop on empty.

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

How to create a mergeable stack — stack is LIFO: push/pop from the same end.

DefHow to create a mergeable stack — Zara uses it for undo typing in a tiny editor.
RuleHow to create a mergeable stack → push / pop LIFO.
RememberHow to create a mergeable stack + a dry-run table (a tiny editor).
UseHow to create a mergeable stack in a tiny editor (undo typing).
TrapHow to create a mergeable stack — pop on empty.
ExHow to create a mergeable stack → undo typing.