Balanced brackets in string

Given a string of brackets, determine if every opening bracket has a matching closing bracket in the correct order.

stack string parsing validation

Write a function `is_balanced(s: str) -> bool` that returns `True` if the input string `s` contains only properly matched and nested brackets `()`, `[]`, and `{}`, and `False` otherwise. A string is balanced if:
- Every opening bracket has a corresponding closing bracket of the same type later in the string.
- Brackets close in the correct order (e.g., `([)]` is **not** balanced).
- All characters in the string are brackets; there are no other characters.

Examples:
- `is_balanced("")` → `True` (empty string has no brackets, so it is balanced).
- `is_balanced("()[]{}``) → `True`
- `is_balanced("([{}])")` → `True`
- `is_balanced("(]")` → `False`
- `is_balanced("([)]")` → `False`
- `is_balanced("{")` → `False`

Constraints

- Input `s` is a string containing only the characters `()[]{}`.
- Length of `s` is between 0 and 10^5.
- Time complexity should be O(n), space complexity O(n).

Example

>>> is_balanced("()[]{}")
True
>>> is_balanced("([{}])")
True
>>> is_balanced("(]")
False
>>> is_balanced("([)]")
False
>>> is_balanced("")
True

10 points ~15 min

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Hints

Use a stack: push opening brackets, pop on closing bracket.

When you see a closing bracket, the top of the stack must match.

At the end, the stack must be empty.

Handle the empty string correctly.

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