Clarify the problem constraints (e.g., only bracket characters, empty string) and then explain the stack-based algorithm: iterate through the string, push opening brackets, and for closing brackets check if the top of the stack matches. After iteration, the stack must be empty for the string to be valid. Walk through a simple example to illustrate, then discuss time and space complexity.
Pro tip: Mention that you can optimize space by using a counter for a single bracket type, but the stack is necessary for multiple types; also discuss early termination when a closing bracket appears with an empty stack. This shows you understand trade-offs and edge cases.
Ask clarifying questions: Are there only bracket characters? What about empty strings? Are there multiple bracket types? Confirm the expected return type (boolean).
Describe using a stack: push opening brackets; for closing brackets, check if stack is non-empty and top matches the corresponding opening bracket, then pop. If not, return false.
Trace through a sample input like '()[]{}' and an invalid one like '([)]' to demonstrate how the stack works and why the order matters.
State that time complexity is O(n) because each character is processed once, and space complexity is O(n) in the worst case (e.g., all opening brackets).
Mention edge cases: empty string (valid), odd length (invalid), and strings with non-bracket characters (if allowed). Optionally, discuss using a hash map for matching pairs and early exit if stack size exceeds half the string length.
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