ruby - Counting changes in a nested array

Question

The status of an alarm is shown in this array. Time format is as follows HH:MM:SS

[["red",    "00:00:00"],
 ["orange", "00:00:02"],
 ["green",  "00:00:05"],
 ["red",    "00:00:07"],
 ["green",  "00:00:27"],
 ["red",    "00:00:28"],
 ["green",  "00:00:29"]]

I would like to count the number of times "red" is followed by "green" within a time period of 10 seconds.

Step 1: Look for red

Step 2: IF Not last item 
           Compare with next item on array
        ELSE Go to Step 4  

Step 3: IF green, 
           time_difference = green_time - red_time 
           IF time_difference <= 10 seconds
                    count = count + 1
                    Go to Step 1
           ELSE Go to Step 1
         ELSE Go to Step 2

Step 4: Print Count

The count should be 2

Answer 1

result =
  input.map do |k, t|
    [k, DateTime.parse(t)]
  end.each_with_object(prev: nil, count: 0) do |(k, t), acc|
    case k
                  # keep the time of the previous occurrence of "red" 
    when "red" then acc[:prev] = t    
    when "green" 
                        # seconds 
      acc[:count] += 1 if 24.0 * 60 * 60 * (t - acc[:prev]) < 10
      acc[:prev] = nil  
    end  
  end[:count]

  p(result)
  #? 2