📐 Problem

Given a string containing only ()[]{}, determine if it’s well-formed: every opening bracket has a matching closing bracket in the correct order.

Java Solution (Stack + Map)

🧠 Complexity

Time: O(n) — each char is pushed/popped at most once.

Space: O(n) — worst case all openings on the stack.

☝️ Takeaway

This question is a perfect showcase for stack thinking: push on open, pop on close, and match pairs. It’s also great for discussing edge cases (odd length, early closing, leftovers) and why a stack beats a simple counter.

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