Micro-Drill #243 — Stack vs queue: LIFO vs FIFO decision

STACK (LIFO) vs QUEUE (FIFO)
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STACK — Last In, First Out:
  "most recent" / "nested" / "matching"
  □ Parentheses matching
  □ Undo/redo
  □ DFS traversal (explicit stack)
  □ Monotonic stack (next greater element)
  □ Expression evaluation
  □ Call stack simulation

QUEUE — First In, First Out:
  "earliest" / "level-by-level" / "waiting line"
  □ BFS traversal (shortest path)
  □ Level-order tree traversal
  □ Task scheduling (FIFO order)
  □ Sliding window max (deque)
  □ Rate limiting (timestamp queue)

DEQUE — both ends:
  □ Sliding window maximum
  □ BFS optimizations
  □ Palindrome check

PRIORITY QUEUE (heap):
  □ "Next best" / "top K" / "median"
  □ Dijkstra, merge K sorted lists