Stack vs Queue (LIFO vs FIFO)

The same operations applied to both containers at once. A stack removes the most recently added item, a queue removes the oldest. That single difference is what separates DFS from BFS, undo from a print spooler.

time push/pop/peek O(1) for both

space O(n)

Input

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Pseudocode

push(v): stack appends to the top;  queue appends to the back
pop():   stack removes the top;      queue removes the front
peek():  stack reads the top;        queue reads the front