X Removal

X Removal

using System;
using System.Collections.Generic;

public class XRemoval
{
    public static void Main()
    {
        List<string> matrix = new List<string>();
        List<bool[]> symbolsToRemove = new List<bool[]>();

        string input = Console.ReadLine();

        while (input != "END")
        {
            matrix.Add(input);
            symbolsToRemove.Add(new bool[input.Length]);

            input = Console.ReadLine();
        }

        for (int row = 0; row < matrix.Count - 2; row++)
        {
            for (int column = 2; column < matrix[row].Length; column++)
            {
                if (matrix[row + 1].Length < column
                    || matrix[row + 2].Length < column + 1)
                {
                    continue;
                }

                char currentSymbol = char.ToLower(matrix[row][column]);

                if (char.ToLower(matrix[row][column - 2]) == currentSymbol
                    && char.ToLower(matrix[row + 1][column - 1]) == currentSymbol
                    && char.ToLower(matrix[row + 2][column - 2]) == currentSymbol
                    && char.ToLower(matrix[row + 2][column]) == currentSymbol)
                {
                    symbolsToRemove[row][column - 2] = true;
                    symbolsToRemove[row][column] = true;
                    symbolsToRemove[row + 1][column - 1] = true;
                    symbolsToRemove[row + 2][column - 2] = true;
                    symbolsToRemove[row + 2][column] = true;
                }
            }
        }

        for (int row = 0; row < matrix.Count; row++)
        {
            for (int column = 0; column < matrix[row].Length; column++)
            {
                if (symbolsToRemove[row][column])
                {
                    continue;
                }

                Console.Write(matrix[row][column]);
            }

            Console.WriteLine();
        }
    }
}