leetcode 228. Summary Ranges

class Solution(object):    def summaryRanges(self, nums):        """        :type nums: List[int]        :rtype: List[str]        """        if not nums:            return []        res = []        last_number = nums[0]        tmp = str(nums[0])        for i in range(1,len(nums)):            if nums[i] == last_number+1:                last_number = nums[i]                continue            else:                if tmp != str(last_number):                    tmp += '->'+str(last_number)                    res.append(tmp)                tmp = str(nums[i])                last_number = nums[i]        if last_number == nums[len(nums)-1] and tmp != str(last_number):            tmp += '->'+str(last_number)        res.append(tmp)        return res