Problem

In a Google code review for embedded firmware, a common low-level correctness check is verifying that delimiters are balanced before deeper parsing. Write a function that determines whether a source string has valid and properly nested brackets.

A string is valid if every opening bracket has a matching closing bracket of the same type, and brackets close in the correct order. Consider only these bracket characters: (), [], and {}. Ignore all other characters.

Formal Specification

• Input: a string code
• Output: True if the brackets in code are balanced and properly nested; otherwise False

Examples

Example 1

• Input: code = "if (a[0] == '{') { return; }"
• Output: True
• Explanation: Non-bracket characters are ignored, and the bracket sequence is properly nested.

Example 2

• Input: code = "([)]"
• Output: False
• Explanation: The closing order is incorrect: ) appears before ] can close [.

Constraints

• 0 <= len(code) <= 10^5
• code may contain ASCII letters, digits, whitespace, operators, and punctuation
• Only (, ), [, ], {, } affect validity
• The solution should run in linear time and be easy to unit test