A chess club wants posters showing every way to put n queens on an n x n board so that no two
queens share a row, a column, or a diagonal. Return all such boards. Each board is a list of n
strings, one per row from top to bottom, using "Q" for a queen and "." for an empty square. The
boards may be returned in any order.
Examples
Input: n = 4
Output: [[".Q..", "...Q", "Q...", "..Q."],
["..Q.", "Q...", "...Q", ".Q.."]]
Input: n = 1
Output: [["Q"]]
Input: n = 3
Output: []
Constraints
1 <= n <= 8
Goals
- Place one piece per row and track attacked columns and diagonals in sets
- Convert each placement into a printable board