summary_ranges.py

from typing import List


class Solution:
    def summaryRanges(self, nums: List[int]) -> List[str]:
        ranges = []
        for n in nums:
            if ranges and ranges[-1][1] == n - 1:
                ranges[-1][1] = n
            else:
                ranges.append([n, n])

        return [f"{x}->{y}" if x != y else f"{x}" for x, y in ranges]