Check balanced parentheses with multiple bracket types

Given a string containing only parentheses '()', determine whether it is balanced. Follow-up: extend the solution to also support '[]' and '{}' with correct nesting and ordering. Describe the algorithm, the data structures you would use (e.g., a stack), time and space complexity, and how you would handle edge cases such as empty strings or unexpected characters.

Check Balanced Parentheses with Multiple Bracket Types

Given a string s containing bracket characters, determine whether the brackets are balanced. A string is balanced when every opening bracket has a corresponding closing bracket of the same type, brackets are closed in the correct (LIFO) order, and there are no stray closing brackets.

Start with only round parentheses (), then extend the same approach to also support square [] and curly {} brackets with correct nesting and ordering.

For this challenge, treat ANY character that is not one of the six bracket characters ()[]{} as invalid input, so the string is considered NOT balanced if it contains one. The empty string is considered balanced.

Return true if the string is balanced, otherwise false.

Examples:

• "()" -> true
• "()[]{}" -> true
• "(]" -> false (mismatched types)
• "([)]" -> false (wrong closing order)
• "{[]}" -> true (correctly nested)
• "" -> true (empty)
• "a(b)c" -> false (unexpected character)

Constraints

• 0 <= len(s) <= 10^4
• s may contain the characters ()[]{} and possibly other characters
• Any character outside the six bracket characters makes the string invalid (not balanced)
• The empty string is balanced

Hints

1. Use a stack: push every opening bracket as you scan left to right.
2. When you hit a closing bracket, the top of the stack must be the matching opening bracket of the same type; otherwise the string is unbalanced.
3. After scanning the whole string, the stack must be empty — leftover opening brackets mean it is unbalanced. Also reject any character that is not one of ()[]{}.