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Summary Ranges

Problem Statement​

You are given a sorted unique integer array nums.

A range [a,b] is the set of all integers from a to b (inclusive).

Return the smallest sorted list of ranges that cover all the numbers in the array exactly. That is, each element of nums is covered by exactly one of the ranges, and there is no integer xsuch thatxis in one of the ranges but not innums.

Each range [a,b] in the list should be output as:

  • "a->b" if a != b
  • "a" if a == b

Leetcode Link

Example 1:​

Input: nums = [0,1,2,4,5,7]
Output: ["0->2","4->5","7"]
Explanation: The ranges are:
[0,2] --> "0->2"
[4,5] --> "4->5"
[7,7] --> "7"

Example 2:​

Input: nums = [0,2,3,4,6,8,9]
Output: ["0","2->4","6","8->9"]
Explanation: The ranges are:
[0,0] --> "0"
[2,4] --> "2->4"
[6,6] --> "6"
[8,9] --> "8->9"

Constraints:​

  • 0 <= nums.length <= 20
  • -231 <= nums[i] <= 231 -1
  • All the values of nums are unique.
  • nums is sorted in ascending order.

Code​

Python Code

class Solution:
    def summaryRanges(self, nums: List[int]) -> List[str]:
        ranges = []
        for n in nums:
            if not ranges or n > ranges[-1][-1] + 1:
                ranges += [],
            ranges[-1][1:] = n,
        return ['->'.join(map(str, r)) for r in ranges]