LeetCode 51 N-Queens - Problem Statement

Place $n$ queens on an $n \times n$ chessboard so no two queens attack each other.

Queens attack horizontally, vertically, and diagonally.

For $n = 4$, one solution:

. Q . .
. . . Q
Q . . .
. . Q .

Return all distinct solutions. Each solution is a board configuration.

Constraints: $1 \le n \le 9$.