Lecture Notes on 27 July 2016

public class Array2D
{
  // determines if a square 2-D array is magic
  public static boolean isMagic (int[][] a)
  {
    int dim = a.length;
    int canon_sum = dim * (1 + dim * dim) / 2;

    // sum the rows of a and see if they are equal to the canon_sum
    for (int i = 0; i < a.length; i++)
    {
      int sum = 0;
      for (int j = 0; j < a[i].length; j++)
      {
        sum += a[i][j];
      }
      if (sum != canon_sum)
        return false;
    }

    // sum the columns and check if they are equal to the canon_sum
    for (int j = 0; j < a[0].length; j++)
    {
      int sum = 0;
      for (int i = 0; i < a.length;i++)
      {
        sum += a[i][j];
      }
      if (sum != canon_sum)
        return false;
    }

    // sum the LR diagonal of a and check
    int sumLR = 0;
    for (int i = 0; i < a.length; i++)
    {
      sumLR += a[i][i];
    }
    if (sumLR != canon_sum)
      return false;

    // sum the RL diagonal of a and check
    int sumRL = 0;
    for (int i = 0; i < a.length; i++)
    {
      sumRL += a[i][a.length - 1 - i];
    }
    if (sumRL != canon_sum)
      return false;

    // passed all the tests
    return true;
  }

  public static int[][] transpose (int[][] a)
  {
    int[][] b = new int [a[0].length][a.length];
    for (int i = 0; i < a.length; i++)
    {
      for (int j = 0; j < a[i].length; j++)
      {
        b[j][i] = a[i][j];
      }
    }
    return b;
  }

  public static int[][] matrixAdd (int[][] a, int[][] b)
  {
    int[][] c = new int [a.length][a[0].length];
    for (int i = 0; i < a.length; i++)
    {
      for (int j = 0; j < a[i].length; j++)
      {
        c[i][j] = a[i][j] + b[i][j];
      }
    }
    return c;
  }

  public static void copyArray (int[][] a, int[][] b)
  {
    for (int i = 0; i < a.length; i++)
    {
      for (int j = 0; j < a[i].length; j++)
      {
        b[i][j] = a[i][j];
      }
    }
  }

  public static void fillArray (int[][] a, int x)
  {
    for (int i = 0; i < a.length; i++)
    {
      for (int j = 0; j < a[i].length; j++)
      {
        a[i][j] = x;
      }
    }
  }

  public static void main (String[] args)
  {
    int[][] a = new int [10][10];

    fillArray (a, -1);

    int[][] b = new int [a.length] [a[0].length];

    copyArray (a, b);
  }
}