rangeExtrac.py

# 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. It is not considered a range unless it spans at least 3 numbers. For example "12,13,15-17"
# Complete the solution so that it takes a list of integers in increasing order and returns a correctly formatted string in the range format.

# Example:

# solution([-10, -9, -8, -6, -3, -2, -1, 0, 1, 3, 4, 5, 7, 8, 9, 10, 11, 14, 15, 17, 18, 19, 20])
# # returns "-10--8,-6,-3-1,3-5,7-11,14,15,17-20"

def solution(args):
    result = ""

    while len(args) > 0:
        first = last = args.pop(0)
        while (len(args) > 0) and (args[0] == last + 1):
            last = args.pop(0)

        if first == last:
            result += f"{first},"
        elif last - first == 1:
            result += f"{first},{last},"
        else:
            result += f"{first}-{last},"
    
    return result[:-1]