function solveNQueens(n, colSet = new Set(), posDiagSet = new Set(), negDiagSet = new Set()) {
    const board = new Array(n).fill().map(() => new Array(n).fill('.'));

    return dfs(board, n, colSet, posDiagSet, negDiagSet);
}
https://leetcode.com/problems/n-queens/
Time O(N!) | Space O(N^2)
@param {number} n
@return {string[][]}