Stacks & Queues intro time O(1) per op space O(n)
Stack — Push & Pop
A stack only ever touches its top. Push puts a value on top; pop takes the top one off. The most recently added value is always the first to leave — last in, first out.
A stack grows upward. Values go on the top and come off the top.
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Practice
Machine twin: /dsa-viz-v2/stack-push-pop.json — the full deterministic run as structured data.