Range extraction

# title: Range extraction
# source: https://rosettacode.org/wiki/Range_extraction
# category: Rosetta Code
# difficulty: Medium
# summary: Compress an ordered list of integers into Rosetta Code's comma-and-range string format.
# tags: popular, strings, formatting, arrays
# vibe: 0.2

def range_extraction(values)
  parts = []
  index = 0

  while index < values.size
    start_value = values[index]
    finish_value = start_value

    while index + 1 < values.length && values[index + 1] == values[index] + 1
      index = index + 1
      finish_value = values[index]
    end

    if finish_value - start_value >= 2
      parts = parts.push("" + start_value + "-" + finish_value)
    elsif finish_value - start_value == 1
      parts = parts.push("" + start_value)
      parts = parts.push("" + finish_value)
    else
      parts = parts.push("" + start_value)
    end

    index = index + 1
  end

  parts.join(",")
end

def run
  range_extraction([
    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
  ])
end