Validate parentheses with one or three bracket types
Company: LinkedIn
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Technical Screen
## Problem
Given a string `s` consisting only of bracket characters, determine whether it is **valid**.
A string is valid if:
- Every opening bracket has a corresponding closing bracket of the same type.
- Brackets are closed in the correct order.
### Part A (initial version)
`s` contains only `'('` and `')'`.
### Part B (follow-up)
`s` may contain three types of brackets: `'()'`, `'[]'`, `'{}'`.
## Input / Output
- **Input:** `s` (string)
- **Output:** `true` if `s` is valid, otherwise `false`
## Constraints (typical)
- `0 <= |s| <= 2 * 10^5`
## Examples
- `s = "()"` → `true`
- `s = "(()"` → `false`
- `s = "([{}])"` → `true`
- `s = "([)]"` → `false`
## Discussion prompts
- Compare using a **stack** vs using a **counter** (for Part A only). When is a counter sufficient, and why does it fail for Part B?
Quick Answer: This question evaluates understanding of string parsing and abstract data structures—particularly stack behavior—and the ability to reason about matching and nesting of brackets within the Coding & Algorithms domain.