py_bracket_validator — Balanced Bracket Checker

Difficulty: medium

Write a function that checks if brackets [], parentheses (), and braces {} are properly balanced and correctly nested in a string. All other characters are ignored. Return True if balanced, False otherwise.

def bracket_validator(s: str) -> bool:

Examples

>>> bracket_validator("()")
True

>>> bracket_validator("()[]{}")
True

>>> bracket_validator("(]")
False

>>> bracket_validator("([)]")
False

>>> bracket_validator("{[]}")
True

>>> bracket_validator("hello(world)[test]{code}")
True

>>> bracket_validator("((()))")
True

>>> bracket_validator("((())")
False

>>> bracket_validator("")
True

Solution

Download py_bracket_validator.py

def bracket_validator(s: str) -> bool:
    pairs = {")": "(", "]": "[", "}": "{"}
    openers = set("([{")
    stack = []
    for ch in s:
        if ch in openers:
            stack.append(ch)
        elif ch in pairs:
            if not stack or stack[-1] != pairs[ch]:
                return False
            stack.pop()
    return not stack

How It Works

Goal: Verify every opening bracket has a matching closer in the correct order.

Approach: Use a stack — push openers, and on a closer pop and check it matches the most recent opener.

Step by step:

1. For each character, ignore anything that is not a bracket character.
2. On an opener ((, [, {), push it onto the stack.
3. On a closer (), ], }), check that the top of the stack is the matching opener. If not (or the stack is empty), return False.
4. After scanning, the stack must be empty — otherwise an opener was never closed.

Key concept: Stacks are the natural data structure for matching nested pairs because the most recently opened context is always the first that must be closed (LIFO).