new_contents: """Leetcode 51. N-Queens.
  Hard.
  
  URL: https://leetcode.com/problems/n-queens/
  
  The n-queens puzzle is the problem of placing n queens on an n×n chessboard 
  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.
  
  Example:
  Input: 4
  Output: [
   [".Q..",  // Solution 1
    "...Q",
    "Q...",
    "..Q."],
  
   ["..Q.",  // Solution 2
    "Q...",
    "...Q",
    ".Q.."]
  ]
  Explanation: There exist two distinct solutions to the 4-queens puzzle 
  as shown above.
  """
  
  class Solution(object):
      def solveNQueens(self, n):
          """
          :type n: int
          :rtype: List[List[str]]
          """
          pass
  
  
  def main():
      pass
  
  
  if __name__ == '__main__':
      main()
  
subject: Add lc051_n_queens.py