TextGravity

namespace TextGravity
{
    using System;
    using System.Text;
    using System.Security;

    public class TextGravity
    {
        public static void Main()
        {
            int numberOfColumns = int.Parse(Console.ReadLine());
            string inputLine = Console.ReadLine();
            int numberOfRows = inputLine.Length / numberOfColumns;

            if (inputLine.Length % numberOfColumns != 0)
            {
                numberOfRows++;
            }

            char[,] matrix = new char[numberOfRows, numberOfColumns];

            //Fill the matrix
            int currentCharIndex = 0;

            for (int row = 0; row < matrix.GetLength(0); row++)
            {
                for (int col = 0; col < matrix.GetLength(1); col++)
                {
                    if (currentCharIndex < inputLine.Length)
                    {
                        matrix[row, col] = inputLine[currentCharIndex];
                        currentCharIndex++;
                    }

                    else
                    {
                        matrix[row, col] = ' ';
                    }
                }
            }

            //Text fall
            for (int col = 0; col < matrix.GetLength(1); col++)
            {
                RunGravity(matrix, col);
            }

            //Print
            StringBuilder outputBuilder = new StringBuilder();
            outputBuilder.Append("<table>");

            for (int row = 0; row < matrix.GetLength(0); row++)
            {
                outputBuilder.Append("<tr>");

                for (int col = 0; col < matrix.GetLength(1); col++)
                {
                    outputBuilder.AppendFormat("<td>{0}</td>",
                        SecurityElement.Escape(matrix[row, col].ToString()));
                }

                outputBuilder.Append("</tr>");
            }

            outputBuilder.Append("</table>");

            Console.WriteLine(outputBuilder.ToString());
        }

        //Method for falling
        private static void RunGravity(char[,] matrix, int col)
        {
            while (true)
            {
                bool hasFalen = false;

                for (int row = 1; row < matrix.GetLength(0); row++)
                {
                    char topChar = matrix[row - 1, col];
                    char currentChar = matrix[row, col];

                    if (currentChar == ' ' && topChar != ' ')
                    {
                        matrix[row, col] = topChar;
                        matrix[row - 1, col] = ' ';
                        hasFalen = true;
                    }
                }

                if (! hasFalen)
                {
                    break;
                }
            }
        }
    }
}