using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        NQueen nQueen = new NQueen();

        nQueen.Slove(8);

    }

}

​

public class NQueen

{

    private int length = 0;

    List<int> rowPlacements; // rowPlacements[x] = y, means placing queen on row: x, column: y

    List<IList<string>> ans = new List<IList<string>>();

​

    public void Slove(int n)

    {

        length = n;

        rowPlacements = Enumerable.Repeat(-1, length).ToList();

​

        DFS(0);

        PrintAnswer();

    }

​

    private void DFS(int row)

    {

        if (row < length)

        {

            for (int col = 0; col < length; col++)

            {

                if (IsSafeToPlace(row, col))

                {

                    rowPlacements[row] = col;

                    DFS(row + 1);

                    rowPlacements[row] = -1;

                }

            }

        }

        else

        {

            PushToAns();

        }

    }

​

    private bool IsSafeToPlace(int row, int col)

    {

        for (int r = 0; r < length; r++)

        {

            if (rowPlacements[r] != -1 &&

                (rowPlacements[r] == col ||

                 r + rowPlacements[r] == row + col ||

                 r - rowPlacements[r] == row - col))

            {

                return false;

            }

        }

        return true;

    }

​

    private void PushToAns()

    {

        List<string> list = new List<string>();

        for (int i = 0; i < length; i++)

        {

            List<string> rowList = Enumerable.Repeat(".", length).ToList();

            rowList[rowPlacements[i]] = "Q";

            list.Add(string.Join("", rowList));

        }

        ans.Add(list);

    }

​

    private void PrintAnswer()

    {

        for (int i = 0; i < ans.Count(); i++)

        {

            Console.WriteLine(string.Format("{1}// Solution {0}", i + 1, Environment.NewLine));

            Console.WriteLine(string.Join(Environment.NewLine, ans[i]));

        }

    }

}