Balanced Brackets

Implement solve(str) that returns true when every opening bracket in
str is closed by the correct matching bracket in the correct order, and
false otherwise.

Supported pairs: () [] {}

Non-bracket characters are ignored.

Examples

solve("({[]})")  → true
solve("()[]{}")  → true
solve("([)]")    → false   // interleaved — wrong order
solve("{[]")     → false   // unclosed opening
solve("")        → true    // empty string is balanced

Approach
Use a stack: push each opening bracket; on a closing bracket, pop and verify
the match. Return true only if the stack is empty at the end.

Constraints

• Input may contain any Unicode characters; only ()[]{} matter.
• Do NOT use a counter — counters cannot detect interleaved mismatches like ([)].