Valid Parentheses

Problem
Given a string containing only the bracket characters ()[]{}, determine whether it is well-formed: every opening bracket is closed by a matching bracket of the same type, and brackets are closed in the correct (properly nested) order.

Input / Output

• Input: a string s of bracket characters.
• Output: true if the brackets are balanced and correctly nested, false otherwise.

Constraints

• 1 <= |s| <= 10^4.
• The string contains only the six bracket characters.

Example

• "([{}])" -> true
• "([)]" -> false (closing order is wrong even though counts match)
• "(" -> false (unclosed)