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

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

Place Non-Attacking Queens | Bytedance Coding Question

Quick Overview

This question evaluates a candidate's competency in combinatorial search, constraint reasoning, and algorithmic design for arranging non-attacking pieces on a grid.

Place Non-Attacking Queens

Company: Bytedance

Role: Site Reliability Engineer

Category: Coding & Algorithms

Difficulty: hard

Interview Round: Technical Screen

Given an integer `n`, return all valid configurations for placing `n` queens on an `n x n` chessboard so that no two queens attack each other. A queen attacks another queen if they share the same row, column, main diagonal, or anti-diagonal. Represent each board configuration as a list of `n` strings of length `n`, where `'Q'` represents a queen and `'.'` represents an empty square. Return the configurations in any order. Example: ```text Input: n = 4 Output: [ [".Q..", "...Q", "Q...", "..Q."], ["..Q.", "Q...", "...Q", ".Q.."] ] ``` Constraints: ```text 1 <= n <= 9 ``` After implementing the solution, analyze its time and space complexity.

Quick Answer: This question evaluates a candidate's competency in combinatorial search, constraint reasoning, and algorithmic design for arranging non-attacking pieces on a grid.

Given an integer n, return all valid configurations for placing n queens on an n x n chessboard so that no two queens attack each other. A queen attacks another queen if they share the same row, column, main diagonal, or anti-diagonal. Represent each configuration as a list of n strings of length n, where 'Q' represents a queen and '.' represents an empty square. Return the configurations in any order.

Constraints

1 <= n <= 9
Each configuration must place exactly one queen in every row
No two queens may share a column, main diagonal, or anti-diagonal

Examples

Input: 1

Expected Output: [["Q"]]

Explanation: On a 1x1 board, the only valid configuration is to place the queen in the single available cell.

Input: 2

Expected Output: []

Explanation: There is no way to place 2 queens on a 2x2 board without them attacking each other.

Input: 3

Expected Output: []

Explanation: There is no valid arrangement for 3 queens on a 3x3 board.

Input: 4

Expected Output: [[".Q..", "...Q", "Q...", "..Q."], ["..Q.", "Q...", "...Q", ".Q.."]]

Explanation: These are the two valid 4x4 boards produced by placing queens row by row from left to right.

Hints

Try placing queens row by row. Once you decide a row, you only need to check whether a column or diagonal is already occupied.
A cell (row, col) belongs to main diagonal (row - col) and anti-diagonal (row + col). These values can be tracked in sets for O(1) conflict checks.

Last updated: May 15, 2026

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