matrix.rb

require 'minitest/autorun'

class Matrix

  # @param {Integer[][]} matrix
  # @return {Boolean}
  def toeplitz?(matrix)
    return false if square?(matrix)

    matrix.each_with_index do |row, row_index|
      row.each_with_index do |value, column_index|
        return false unless value.is_a? Integer
        
        diagonal_value = matrix[row_index-1][column_index-1]
        if row_index > 0 && column_index > 0 && value != diagonal_value
          return false
        end
      end
    end
    
    true
  end

  private
  # @param {Integer[][]} matrix
  # @return {Boolean}
  def square?(matrix)
    matrix.size > 0 && matrix.size == matrix.first.size
  end
end

class MatrixTest < MiniTest::Unit::TestCase
  def setup
    @matrix = Matrix.new
  end
  
  def test_valid_toeplitz_matrix
    input = [
      [1, 2, 3, 4],
      [5, 1, 2, 3],
      [4, 5, 1, 2],
      [7, 4, 5, 1]
    ]
    assert_equal @matrix.toeplitz?(input), true
  end

  def test_invalid_toeplitz_matrix
    input = [
      [1, 2, 3, 4],
      [5, 1, 6, 3],
      [4, 5, 1, 2],
      [7, 4, 5, 1]
    ]
    assert_equal @matrix.toeplitz?(input), false
  end

  def test_non_square_matrix
    input = [
      [1, 2, 3, 4],
      [5, 1, 2, 3],
      [4, 5, 1, 2]
    ]
    assert_equal @matrix.toeplitz?(input), false
  end
end