# The n-queens puzzle is the problem of placing n queens on
# an nxn chess board such that no two queens attack each other.
#
# Given an integer n, return all distinct solutions to the n-queens puzzle.
#
# Each solution contains a distinct board configuration of the n-queens' placement,
# where 'Q' and '.' both indicate a queen and an empty space respectively.
#
# For example,
# There exist two distinct solutions to the 4-queens puzzle:
#
# [
# [".Q..", // Solution 1
# "...Q",
# "Q...",
# "..Q."],
#
# ["..Q.", // Solution 2
# "Q...",
# "...Q",
# ".Q.."]
# ]