Matrix Rotation - study the code

matrixRotation6.cs

using System;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.IO;
using System.Numerics;
using System.Collections;
using System.Collections.Generic;

static class Program
{
    static void Main(string[] args)
    {
        string[] parts = Console.ReadLine().Split(' ');
        int m = Convert.ToInt32(parts[0]);
        int n = Convert.ToInt32(parts[1]);
        long r = Convert.ToInt64(parts[2]);

        long[,] matrix = new long[m, n];

        for (int row = 0; row < m; row++)
        {
            parts = Console.ReadLine().Split(' ');
            for (int col = 0; col < parts.Length; col++)
            {
                matrix[row, col] = Convert.ToInt64(parts[col]);
            }
        }

        int limit = Math.Min(m, n) / 2;
        for (int i = 0; i < limit; i++)
        {
            long[] layer = ReadLayerInMatrix(matrix, m, n, i, i);
            RotateLayer(layer, r);
            WriteLayerInMatrix(matrix, m, n, i, i, layer);
        }

        for (int row = 0; row < m; row++)
        {
            for (int col = 0; col < n; col++)
            {
                Console.Write("{0} ", matrix[row, col]);
            }
            if (row != m - 1)
            {
                Console.WriteLine();
            }
        }
    }

    static void WriteLayerInMatrix(long[,] matrix,
                                   int m,
                                   int n,
                                   int startRow,
                                   int startCol,
                                   long[] layer)
    {
        int index = 0;
        for (int c = startCol; c <= n - startCol - 1; c++)
        {
            matrix[startRow, c] = layer[index++];
        }
        for (int r = startRow + 1; r <= m - startRow - 1; r++)
        {
            matrix[r, n - startCol - 1] = layer[index++];
        }
        for (int c = n - startCol - 2; c >= startCol; c--)
        {
            matrix[m - startRow - 1, c] = layer[index++];
        }
        for (int r = m - startRow - 2; r > startRow; r--)
        {
            matrix[r, startCol] = layer[index++];
        }
    }

    static long[] ReadLayerInMatrix(long[,] matrix,
                                    int m,
                                    int n,
                                    int startRow,
                                    int startCol)
    {
        int lenOutputArray = 2 * (m - 2 * startRow) + 2 * (n - 2 * startCol - 2);
        long[] layer = new long[lenOutputArray];

        int index = 0;
        for (int c = startCol; c <= n - startCol - 1; c++)
        {
            layer[index++] = matrix[startRow, c];
        }
        for (int r = startRow + 1; r <= m - startRow - 1; r++)
        {
            layer[index++] = matrix[r, n - startCol - 1];
        }
        for (int c = n - startCol - 2; c >= startCol; c--)
        {
            layer[index++] = matrix[m - startRow - 1, c];
        }
        for (int r = m - startRow - 2; r > startRow; r--)
        {
            layer[index++] = matrix[r, startCol];
        }

        return layer;
    }


    static void RotateLayer(long[] layer,
                            long r)
    {
        long[] layerTemp = new long[layer.Length];

        for (int i = 0; i < layer.Length; i++)
        {
            int index = (int)((i - r) % layer.Length);
            if(index < 0)
            {
                index += layer.Length;
            }
            layerTemp[index] = layer[i];
        }

        for (int i = 0; i < layer.Length; i++)
        {
            layer[i] = layerTemp[i];
        }
    }
}