my-solutions/problems/1582-special-positions-in-a-binary-matrix/main.rb

# @param {Integer[][]} mat
# @return {Integer}
def num_special(mat)
  count = 0

  mat.each_with_index do |row, i|
    row.each_with_index do |cell, j|
      count += 1 if cell == 1 && special?(mat, i, j)
    end
  end

  count
end

def special?(mat, row_index, column_index)
  mat[row_index].each_with_index do |cell, x|
    return false if cell == 1 && x != column_index
  end

  mat.each_with_index do |row, x|
    return false if row[column_index] == 1 && x != row_index
  end

  true
end