边工作边刷题：70天一遍leetcode: day 72

Missing Range

要点：题简单，这类题的特点都是记录上一步的状态，比如这题是end

错误点：

• 三种情况：一是连续的，即和上一个end差1，而是中间只差1个数，没有’->'，最后是大于1，有’->'
• 看清题：upper/lower是boundary，不一定出现在nums里。为了统一，把upper+1放入nums，同时初始end=lower-1
• 区间是[end+1, num-1]
• 别忘了每次更新end

https://repl.it/Cjvy/2

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

# For example, given [0, 1, 3, 50, 75], lower = 0 and upper = 99, return ["2", "4->49", "51->74", "76->99"].

# Hide Company Tags Google
# Hide Tags Array
# Hide Similar Problems (M) Summary Ranges

class Solution(object):
    def findMissingRanges(self, nums, lower, upper):
        """
        :type nums: List[int]
        :type lower: int
        :type upper: int
        :rtype: List[str]
        """
        end = lower
        res = []
        for num in nums+[upper+1]:
            if num!=end:
                if num-1!=end:
                    res.append("{}->{}".format(end, num-1))
                else:
                    res.append(str(num-1))
            end = num+1 # error: don't forget

        return res

sol = Solution()
assert sol.findMissingRanges([0, 1, 3, 50, 75], 0, 99)==['2', '4->49', '51->74', '76->99']