summary_ranges.rb

def summary_ranges(nums)
  res = []
  l = nums.length
  return [str(nums[0])] if l == 1
  i = 0
  while i < l
    start = nums[i]
    i += 1 while (i + 1 < l) && (nums[i + 1] - nums[i] == 1)
    if nums[i] != start
      res.push(start.to_s + '->' + nums[i].to_s)
    else
      res.push(start.to_s)
    end
    i += 1
  end
  res
end

a = [0, 1, 2, 4, 5, 7]
p('input: ')
p(a)
p('output should be')
p(['0->2', '4->5', '7'])
p('output: ')
p(summary_ranges(a))