Summary ranges

We will iterate over the array and find the ranges. Then we will map the ranges to the required format.

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]

Time complexity: O(n)
Space complexity: O(n)