163. Missing-Ranges.md

Description

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

Example:

Input: nums = [0, 1, 3, 50, 75], lower = 0 and upper = 99,
Output: ["2", "4->49", "51->74", "76->99"]

---

这道题规定了nums所有值都在[lower，upper]区间，使得这道题难度降低许多。

我们只需要将lower + 1 插到nums头部，把upper - 1插到nums末尾，然后遍历数组就可以了，缺失的区间是num[i]+1 ~ num[i+1]-1。

python solution

class Solution(object):
    def findMissingRanges(self, nums, lower, upper):
        """
        :type nums: List[int]
        :type lower: int
        :type upper: int
        :rtype: List[str]
        """
        nums.insert(0, lower - 1)
        nums.append(upper + 1)
        res = []
        for i in range(len(nums) - 1):
            left, right = nums[i], nums[i + 1]
            if left < right - 1: # 确保right和left之间差 >=2 ，这样才有可能插入区间
                if right - left == 2:
                    res.append(str(right - 1))
                else:
                    res.append(str(left + 1) + "->" + str(right - 1))
        return res