class Solution(object):
def findMissingRanges(self, nums, lower, upper):
"""
:type nums: List[int]
:type lower: int
:type upper: int
:rtype: List[str]
"""
ranges = []
prev = lower - 1
for i in range(len(nums) + 1):
if i == len(nums):
curr = upper + 1
else:
curr = nums[i]
if curr - prev > 2:
ranges.append("%d->%d" % (prev + 1, curr - 1))
elif curr - prev == 2:
ranges.append("%d" % (prev + 1))
prev = curr
return ranges
