Lesson 032
Stack Operations
Push · Pop · Peek
1:00How a stack's three O(1) operations — push, pop, and peek — work, when they fail, and where they power real programs.
By the end, you can
- Explain the LIFO property and why all access happens at the top.
- Trace the exact state of a stack after any sequence of push, pop, and peek operations.
- Write or explain the push, pop, and peek algorithms including their guard conditions.
- State what `top` holds for an empty stack and derive the size from `top`.
- Distinguish underflow from overflow and identify the correct guard for each.
- Give the time complexity of push, pop, peek, and isEmpty, and explain why they are O(1).
- Contrast array-backed and linked-list-backed stacks and their trade-offs.
- Describe how the call stack, balanced-bracket checking, undo systems, and DFS each rely on the push/pop pattern.
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