def gridlandMetro(n, m, k, track)
    minMax = Hash.new(-1)
    track.each do |line|
        minMax[line[0]] = [] if minMax[line[0]] == -1            
        minMax[line[0]] << [line[1], line[2]] 
    end
    counter = 0
    minMax.values.each do |line|
        line.sort!        
        while not line.empty?
            start_point, end_point = line.shift        
            end_point = [line.shift[1], end_point].max while not line.empty? and line[0][0] <= end_point
            counter += end_point - start_point + 1
        end        
    end
    m*n - counter
end