Description:

Given a sorted integer array where the range of elements are in the inclusive range [lower, upper], return its missing ranges.

Example
Example 1

Input:

nums = [0, 1, 3, 50, 75], lower = 0 and upper = 99
Output:
["2", "4->49", "51->74", "76->99"]
Explanation:
in range[0,99],the missing range includes:range[2,2],range[4,49],range[51,74] and range[76,99]

Example 2

Input:
nums = [0, 1, 2, 3, 7], lower = 0 and upper = 7
Output:
["4->6"]
Explanation:
in range[0,7],the missing range include range[4,6]

Solution: 很无聊的一道题，各种corner cases

NTOE: 刚开始只是把lower和upper+1输入到nums里，后来评论区提醒，要把lower-1替换lower

class Solution:
    """
    @param: nums: a sorted integer array
    @param: lower: An integer
    @param: upper: An integer
    @return: a list of its missing ranges
    """
    def findMissingRanges(self, nums, lower, upper):
        # write your code here
        
        def helper(l,h):
            if l == h:
                return str(l)
            else:
                return str(l) + "->" + str(h)
         
        if not nums:
            return [helper(lower,upper)]
                
        nums = [lower-1] + nums + [upper+1]
        
        ret = []
        for i in range(1,len(nums)):
            n1,n2 = nums[i-1],nums[i] 
            if n2 > n1+1:
                ret.append(helper(n1+1,n2-1))
                
        if not ret:
            if lower == nums[1]:
                return []
            else:
                return [helper(lower,nums[1])]
        else:
            return ret