Matrix Operations

Versión en español de esta publicación.
Some time ago I was presented with some algorithms common problems related to matrices, today I just found some code in my Windows virtual machine and I through that maybe it was a good idea to publish it here just to keep it online.

I remember I was looking for an algorithm to print a square matrix in spiral, and I found some code in the internet as usual which used a nice approach, I had to modify it because it was in another language and I needed it to be in C#,

Well here is the class I made with the internet approach, the class supports square matrix multiplication and also supports printing a square matrix in spiral using an indirect recursive approach.

Matrices.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
 
namespace Samples
{
    public static class Matrices
    {
        public static double[,] MtxMult(double[,] mtxA, double[,] mtxB)
        {
            if (mtxA == null || mtxA.Length == 0)
                throw new ArgumentException("Array parameter must be valid");
     
            if (mtxB == null || mtxB.Length == 0)
                throw new ArgumentException("Array parameter must be valid");
  
            if (mtxA.Length != mtxB.Length)
                throw new ArgumentException("Arrays must have the same length");
  
            int size = mtxA.GetLength(0); // get first dimmension lenght
            double[,] mtxC = new double[size, size];
            for (int i = 0; i < size; i++)
                for (int j = 0; j < size; j++)
                {
                    // Compute dot product of row i and column j.
                    for (int k = 0; k < size; k++)
                        mtxC[i, j] += mtxA[i, k] * mtxB[k, j];
                }
                 
            return mtxC;
        }
 
        private static IList<int> _spiralMtx = null;
        public static IList<int> MtxProcessSpiral(int[,] mtx)
        {
            _spiralMtx = null;
            _spiralMtx = new List<int>();
            int x1 = 0;
            int y1 = 0;
            int x2 = mtx.GetLength(0) - 1;
            int y2 = mtx.GetLength(1) - 1;
            MtxProcessTopRight(mtx, x1, y1, x2, y2);
            return _spiralMtx;
        }
 
        //
        // prints the top and right shells of the matrix
        //
        private static void MtxProcessTopRight(int[,] mtx, int x1, int y1, int x2, int y2)
        {
            int i = 0; 
            int j = 0;
            // print the row
            for (i = x1; i <= x2; i++)
                _spiralMtx.Add(mtx[y1, i]);
             
            //print the column 
            for (j = y1 + 1; j <= y2; j++)
                _spiralMtx.Add(mtx[j, x2]);
             
            // see if we have more cells left
            if (x2 - x1 > 0 && y2 - y1 > 0)
            {
                // 'recursively' call the function to print the bottom-left layer
                MtxProcessBottomLeft(mtx, x1, y1 + 1, x2 - 1, y2);
            }
        }
 
        //
        // prints the bottom and left shells of the matrix
        //
        private static void MtxProcessBottomLeft(int[,] mtx, int x1, int y1, int x2, int y2)
        {
            int i = 0;
            int j = 0;
            // print the row of the matrix in reverse
            for (i = x2; i >= x1; i--)
                _spiralMtx.Add(mtx[y2, i]);
 
            // print the last column of the matrix in reverse
            for (j = y2 - 1; j >= y1; j--)
                _spiralMtx.Add(mtx[j, x1]);
 
            if (x2 - x1 > 0 && y2 - y1 > 0)
            {
                // 'recursively' call the function to print the top-right layer
                MtxProcessTopRight(mtx, x1 + 1, y1, x2, y2 - 1);
            }
        }
    } 
}

Enjoy! 🙂
-Yohan