给定一个排序的整数数组 nums ，其中元素的范围在 闭区间 [lower, upper] 当中，返回不包含在数组中的缺失区间。
示例：
输入: nums = [0, 1, 3, 50, 75], lower = 0 和 upper = 99, 输出: ["2", "4->49", "51->74", "76->99"] `
class Solution:
def findMissingRanges(self, nums: List[int], lower: int, upper: int) -> List[str]:
res = []
def append_res(start, end):
t = str(start)
if end > start:
t += '->' + str(end)
res.append(t)
for num in nums:
if num > lower:
append_res(lower, num-1)
lower = num+1
if num == upper:
return res
if lower <= upper:
append_res(lower, upper)
return res
a = Solution()
test = [0, 1, 3, 50, 75]
print(a.findMissingRanges(test, 0, 99))
`
