figure out how it works!

Okay. if you look at the code you'll see it essentially consists of 3 consecutive loops:

1. my @expd = map{ ... } @inputs

   This takes an input like ["010000", "010110", 6] and adds two columns to it to make ["010000", "010110", 6, 0, 70].

   Ie. It takes each of the day/hour/minute values and converts them to an integer (dhm2int()) and appends them. This gets all the messy string handling out the way up front and simplifiies all comparisons.

   Also, within that map there is a while loop. Its job is to check to see if the range being integerised spans a day boundary. If it does, it breaks the range into two (or more) ranges as required.

2. The second block consists of two nested for loops that construct two parallel arrays @tally, @id from @expd.
   1. The outer loop runs over the list of ranges.
   2. The inner loop runs from start to the end of the range.
   3. At each position, if the current value at that position on the "tally stick", @tally is undefined, or greater than value of the current range, then replace it with the value from the current range, and record the id(index) of the current range in the parallel array @id

   At the end of the (double) loop @tally looks like this:

   6 6 6 6 6 1 1 1 1 1 1 1 1 1 1 1 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 
   +6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6
   + 6                                                  5 5 5 5 5 5 5 4 4
   + 4 4 4
   
   
                3 3 3 3 3 1 1 1 1 1 1 1 1 1 3 3 3 3 3 3 3 3 3
   [download]

   And @id looks like this:

   0 0 0 0 0 4 4 4 4 4 4 4 4 4 4 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 
   +0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
   + 0                                                  1 1 1 1 1 1 1 5 5
   + 5 5 5
   
   
                2 2 2 2 2 6 6 6 6 6 7 7 7 7 3 3 3 3 3 3 3 3 3
   [download]

   As you can see, we now have a list of the lowest value available for every minute of the period, and the index of the associated range that contributed it. Though the latter information is actually now redundant. Any minute that is not covered by any range has both value and ID as undef and shows up blank above.

   All we need to do is walk our way down the tally stick and convert the start and end index minute of each contiguous range of values back to the corresponding day/hour/minute (int2dhm()) and we can construct the required list of output ranges, in sorted order, without any complex comparison logic.

3. And that's what the final while loop does.