Lesson 031
Stacks Introduction
LIFO · Push · Pop · Peek
1:00A stack is a Last In, First Out container where only the top is ever accessible — push, pop, and peek are all O(1), making it one of computing's most widely used building blocks.
By the end, you can
- Explain the LIFO rule and why the output order is the reverse of the input order.
- Distinguish push, pop, and peek and predict the stack state after any sequence of operations.
- Choose between an array-backed and a linked-list-backed stack and explain the trade-offs.
- Identify underflow and overflow conditions and explain how to prevent each.
- State the time complexities of push, pop, peek, and a stack-interior search, and justify each.
- List four real-world systems that rely on a stack and explain which stack property each exploits.
- Trace the balanced-parentheses algorithm character by character and determine whether a string is balanced.
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