Range extraction

Range extraction
You are encouraged to solve this task according to the task description, using any language you may know.

A format for expressing an ordered list of integers is to use a comma separated list of either

• individual integers
• Or a range of integers denoted by the starting integer separated from the end integer in the range by a dash, '-'. (The range includes all integers in the interval including both endpoints)

So the list of integers: 1, 2, 3, 6, 7, 9 could be written as: 1-3,6-7,9 or as 1-3,6,7,9 or as ...

We add a further rule:

• The range syntax is to be used only for, and for every range that expands to more than two values.

This means that the above example could only become: 1-3,6,7,9

The task is to create a function that takes a list of integers and returns a correctly formatted string in the range format. Use the function to compute and print the range formatted version of the following ordered list of integers:

    0,  1,  2,  4,  6,  7,  8, 11, 12, 14,
   15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
   25, 27, 28, 29, 30, 31, 32, 33, 35, 36,
   37, 38, 39

C.f. Range expansion

Python

<lang python>#import random

def rangeextract(lst):

   lenlst = len(lst)
   i, ranges = 0, []
   while i< lenlst:
       low = lst[i]
       while i <lenlst-1 and lst[i]+1 == lst[i+1]: i +=1
       hi = lst[i]
       ranges.append(
           '%i-%i'  % (low, hi) if hi - low >= 2 else
           ('%i,%i' % (low, hi) if hi - low == 1 else
            '%i' % low) )
       i += 1
   return ','.join(ranges)

1. lst = sorted(random.sample(list(range(40)), 33))
2. print (lst)

lst = [ 0, 1, 2, 4, 6, 7, 8, 11, 12, 14,

      15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
      25, 27, 28, 29, 30, 31, 32, 33, 35, 36,
      37, 38, 39]

print(rangeextract(lst))</lang>