Notes for B2.2.3 Concept of a Stack as a "Last In, First Out" (LIFO) Data Structure - IB | RevisionDojo
B2.2.3 Concept of a Stack as a "Last In, First Out" (LIFO) Data Structure Notes
Understanding Stacks as LIFO Data Structures
A stack is a linear data structure that follows the Last In, First Out (LIFO) principle.
The last item added is the first one removed.
Analogy: Like a stack of plates in a cafeteria—you can only add/remove the plate at the top.
Hint
Always think “last added = first out.”
Common Mistake
Assuming you can directly access elements in the middle (not possible without popping).
Fundamental Stack Operations
Push
Adds an item to the top of the stack.
Time Complexity: O(1)
Pop
Removes and returns the item from the top.
Time Complexity: O(1)
Peek / Top
Returns the top element without removing it.
Time Complexity: O(1)
isEmpty
Checks whether the stack is empty.
Time Complexity: O(1)
Hint
Push/Pop/Peek always work at the top only.
Common Mistake
Forgetting to check isEmpty before pop() → runtime error.
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Note
Understanding Stacks as LIFO Data Structures
A stack is a linear data structure that follows the Last In, First Out (LIFO) principle.
The last item added is the first one removed.
Analogy: Like a stack of plates in a cafeteria—you can only add/remove the plate at the top.
DefinitionStackA linear data structure that follows the Last In, First Out (LIFO) principle.AnalogyThink of a stack like a stack of plates in a cafeteria. You can only add or remove the plate at the top.Common MistakeAssuming you can directly access elements in the middle (not possible without popping).ExampleIf you push the numbers 1, 2, and 3 onto a stack, popping will return 3, then 2, then 1.NoteAlways think "last added = first out."
