Pretty standard stack question but I fumbled the edge cases a bit.
Start by clarifying the problem constraints and edge cases, then explain the stack-based algorithm step-by-step, and finally walk through a concrete example to demonstrate correctness. Emphasize the O(n) time and O(n) space complexity and discuss potential optimizations or alternative approaches.
Pro tip: Mention that you can early-exit if the string length is odd, and that using a hash map for bracket pairs makes the code cleaner and more extensible. Also, discuss how this approach can be adapted for multiple bracket types.
Ask if the string contains only brackets, if empty string is valid, and if there are multiple bracket types. Confirm that O(n) time and O(n) space are required.
Describe iterating through each character: push opening brackets onto the stack; for closing brackets, check if the stack is empty or the top doesn't match, then pop if it matches. At the end, the stack must be empty.
Choose a sample string like '{[()]}' and trace the stack operations to show how it validates correctly. Also show an invalid example like '{[}]' to illustrate failure.
State that time complexity is O(n) because each character is processed once, and space complexity is O(n) in the worst case (all opening brackets). Mention early exit for odd-length strings and using a hash map for bracket pairs.
If required, write the function in a language of your choice, using a stack (e.g., list in Python) and a dictionary for matching pairs. Include comments and handle edge cases.
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