N-Queens

Hard~35 min

The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other.

Given an integer n, return all distinct solutions to the n-queens puzzle. You may return the answer in any order.

Each solution contains a distinct board configuration of the n-queens' placement, where 'Q' and '.' both indicate a queen and an empty space, respectively.

Examples

Example 1

Input: n = 4

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

Explanation: There are exactly 2 distinct solutions for the 4-queens puzzle.

Example 2

Input: n = 1

Output: [["Q"]]

Explanation: A single queen on a 1x1 board is the only solution.

Constraints

1 <= n <= 9
Expected time complexity: O(n!)

Code

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Output

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