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📚 Stack

Stacks shine when you need to "remember the last thing" — matching brackets, evaluating expressions, finding the next greater element. The monotonic stack is the highest-leverage pattern here.

This category contains 9 problems. Use the patterns below to recognize what's being asked, then jump to the problem list at the bottom.

🧠 Key Patterns​

  • Bracket Matching / Validation — Push opens, pop & compare on close.
  • Monotonic Stack — Next greater/smaller element. O(n)O(n) amortized.
  • Expression Evaluation — Shunting yard, postfix evaluation.
  • Min/Max Stack — Auxiliary stack tracking running min/max.
  • Simulating Recursion — Iterative DFS, in-order without recursion.

⚠️ Common Pitfalls​

  • Forgetting to flush remaining elements after the main loop (e.g. unmatched brackets).
  • Monotonic stack: choosing wrong comparison direction.

📚 Study Resources​

📺 Videos​

📖 Books​

  • Algorithms — Sedgewick — Ch. 1.3

🌐 Articles & References​

💻 All Stack Problems​

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