20. Python Chapter 8.4 — stacks - revision mindmap
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The map is a completed revision summary. Cover a branch and reconstruct it, then try the linked chapter practice. Read the image at full size when labels are small.
Text version
Stack contract
- LIFO
- Push adds top; pop removes/returns top
- Peek reads without removal
- Match question’s output and failure convention
Array implementation
- Preallocated storage and logical top
- Last-occupied convention: top starts −1
- Size = top + 1; full at capacity − 1
- Guard before update; save removed value before changing top
Linked implementation
- Top is node reference
- Push at head
- Pop moves top to next
- Singleton removal leaves null; finite memory without fixed array capacity
Applications
- Nested calls and recursion
- Undo most recent action
- Bracket matching: order and type matter
- Postfix evaluates; infix conversion uses precedence/associativity
Expression workflow
- Operand: push
- Operator: pop right then left
- Apply operation and push result
- Parentheses and equal-precedence handling for conversion
Worked example & exam traps
- Push A, push B, pop → returns B; top becomes A.
- Postfix 8 3 - 2 *: [8,3] → [5] → [5,2] → [10].
- For subtraction, first popped = right operand; second popped = left.
- Avoid: first pop as left operand; balanced counts imply balanced brackets
Sources and reading
This map condenses Chapter 20 and its source trail. Use the self-learning reading guide for the corresponding VJC pages and A notes. It does not add topics to the stated promo scope.