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This is a medium difficulty Coding & Algorithms question, commonly asked during Technical Screen rounds at Bytedance.

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This question is commonly asked for Software Engineer candidates at Bytedance during technical interviews.

Validate a bracket string | Bytedance Coding Question

Quick Overview

This question evaluates understanding of stack data structures, string parsing, and matching logic for balanced brackets and parentheses. It is commonly asked in technical interviews within the Coding & Algorithms domain to assess the ability to produce correct and efficient bracket-matching logic, testing practical application of data-structure implementation alongside conceptual understanding of stack behavior and edge-case handling.

Validate a bracket string

Company: Bytedance

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: medium

Interview Round: Technical Screen

Given a string `s` containing only the characters `'('`, `')'`, `'{'`, `'}'`, `'['`, and `']'`, determine whether the input string is valid. A string is valid if: 1. Every opening bracket has a corresponding closing bracket of the same type. 2. Brackets are closed in the correct order. 3. Every closing bracket matches the most recent unmatched opening bracket. Return `true` if `s` is valid; otherwise return `false`. Example: - Input: `"()[]{}"` → Output: `true` - Input: `"([)]"` → Output: `false`

Quick Answer: This question evaluates understanding of stack data structures, string parsing, and matching logic for balanced brackets and parentheses. It is commonly asked in technical interviews within the Coding & Algorithms domain to assess the ability to produce correct and efficient bracket-matching logic, testing practical application of data-structure implementation alongside conceptual understanding of stack behavior and edge-case handling.

Constraints

1 <= s.length <= 10^4 (the empty string is also considered valid).
s consists only of the characters '(', ')', '{', '}', '[' and ']'.

Examples

Input: ("()[]{}",)

Expected Output: True

Explanation: Each opening bracket is immediately closed by a matching closing bracket of the same type.

Input: ("([)]",)

Expected Output: False

Explanation: The ')' tries to close '[', the most recent unmatched opener, so the order is wrong.

Input: ("",)

Expected Output: True

Explanation: An empty string has no unmatched brackets, so it is trivially valid.

Input: ("(",)

Expected Output: False

Explanation: The '(' is never closed; the stack is non-empty at the end.

Input: (")",)

Expected Output: False

Explanation: A closing bracket appears with no opener on the stack to match it.

Input: ("{[]}",)

Expected Output: True

Explanation: Properly nested: '[]' closes inside '{}'.

Input: ("([{}])",)

Expected Output: True

Explanation: Deeply nested brackets all close in the correct reverse order.

Input: ("]",)

Expected Output: False

Explanation: A lone closing bracket with an empty stack is invalid.

Input: ("((",)

Expected Output: False

Explanation: Two openers remain unmatched at the end, so the stack is not empty.

Hints

Use a stack. Push every opening bracket as you encounter it.
When you see a closing bracket, it must match the bracket on top of the stack — if the stack is empty or the top does not match, the string is invalid.
After scanning the whole string, the string is valid only if the stack is empty (no unmatched openers remain).

Last updated: Jun 26, 2026

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Quick Overview

Validate a bracket string

Company: Bytedance

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: medium

Interview Round: Technical Screen

Constraints

1 <= s.length <= 10^4 (the empty string is also considered valid).
s consists only of the characters '(', ')', '{', '}', '[' and ']'.

Examples

Input: ("()[]{}",)

Expected Output: True

Explanation: Each opening bracket is immediately closed by a matching closing bracket of the same type.

Input: ("([)]",)

Expected Output: False

Explanation: The ')' tries to close '[', the most recent unmatched opener, so the order is wrong.

Input: ("",)

Expected Output: True

Explanation: An empty string has no unmatched brackets, so it is trivially valid.

Input: ("(",)

Expected Output: False

Explanation: The '(' is never closed; the stack is non-empty at the end.

Input: (")",)

Expected Output: False

Explanation: A closing bracket appears with no opener on the stack to match it.

Input: ("{[]}",)

Expected Output: True

Explanation: Properly nested: '[]' closes inside '{}'.

Input: ("([{}])",)

Expected Output: True

Explanation: Deeply nested brackets all close in the correct reverse order.

Input: ("]",)

Expected Output: False

Explanation: A lone closing bracket with an empty stack is invalid.

Input: ("((",)

Expected Output: False

Explanation: Two openers remain unmatched at the end, so the stack is not empty.

Hints

Use a stack. Push every opening bracket as you encounter it.
When you see a closing bracket, it must match the bracket on top of the stack — if the stack is empty or the top does not match, the string is invalid.
After scanning the whole string, the string is valid only if the stack is empty (no unmatched openers remain).

Last updated: Jun 26, 2026

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