Start by clarifying the problem: confirm the bracket types (e.g., (), [], {}) and that the string contains only brackets. Then propose a stack-based solution: iterate through the string, push opening brackets onto the stack, and for closing brackets, check if the stack is non-empty and the top matches; finally, ensure the stack is empty. Discuss time and space complexity (O(n) time, O(n) space) and consider edge cases like empty string and unmatched brackets.
Pro tip: Mention that you can optimize space by using a counter for a single bracket type, but for multiple types a stack is necessary. Also, note that early termination when a mismatch occurs can save time.
Ask if the string contains only brackets and which types (e.g., (), [], {}). Confirm that an empty string is considered valid.
Explain that a stack is ideal because brackets must be closed in LIFO order. Mention that a hash map can map closing brackets to opening ones for quick lookup.
Iterate through each character: if it's an opening bracket, push onto stack; if closing, check if stack is empty or top doesn't match, return false; otherwise pop. After loop, return true if stack is empty.
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).
Walk through examples like '()[]{}' (valid), '([)]' (invalid), and '{[]}' (valid) to demonstrate correctness and edge cases.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.