Matrix binary search

matrix_binary_search.rb

class Matrix
  Coordinate = Struct.new(:x, :y)

  def initialize(grid)
    @grid = grid
  end

  def binary_search(n)
    row = find_row(n, 0, grid.count - 1)
    return nil unless row

    col = grid[row].index(n)
    return nil unless col

    Coordinate.new(row, col)
  end

  private

  attr_reader :grid

  def find_row(n, low, high)
    return nil if low > high
    r = (high + low) / 2

    if grid[r][0] <= n
      if r == grid.count - 1 || grid[r + 1][0] > n
        r
      else
        find_row(n, r + 1, high)
      end
    else
      find_row(n, low, r - 1)
    end
  end
end

matrix = Matrix.new([
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50],
  [51, 60, 64, 65],
  [70, 71, 72, 100]
])

puts matrix.binary_search(16) || 'Not found!'
puts matrix.binary_search(50) || 'Not found!'
puts matrix.binary_search(-1) || 'Not found!'
puts matrix.binary_search(100) || 'Not found!'
puts matrix.binary_search(63) || 'Not found!'
puts matrix.binary_search(64) || 'Not found!'