solution.py

from typing import List


class Solution:
    def merge(self, intervals: List[List[int]]) -> List[List[int]]:
        intervals.sort(key=lambda x: x[0])
        res = [intervals[0]]

        for start, end in intervals[1:]:
            lastEnd = res[-1][1]
            if start <= lastEnd:
                res[-1][1] = max(lastEnd, end)
            else:
                res.append([start, end])
        return res


if __name__ == '__main__':
    intervals = [[1, 3], [2, 6], [8, 10], [15, 18]]
    print(Solution().merge(intervals))