merge.py

from typing import List
class Solution:
    def merge(self, intervals: List[List[int]]) -> List[List[int]]:

        intervals.sort(key=lambda x: x[0])

        merged = []
        for interval in intervals:
            # if the list of merged intervals is empty or if the current
            # interval does not overlap with the previous, simply append it.
            if not merged or merged[-1][1] < interval[0]:
                merged.append(interval)
            else:
            # otherwise, there is overlap, so we merge the current and previous
            # intervals.
                merged[-1][1] = max(merged[-1][1], interval[1])

        return merged

# Checking in PyCharm/terminal:
if __name__ == '__main__':
    Instant = Solution()
    Solve = Instant.merge([[1,3],[2,6],[8,10],[15,18]])  # [[1,3],[2,6],[8,10],[15,18]] -> [[1, 6], [8, 10], [15, 18]] | [[1,4],[4,5]] -> [[1,5]]
    print(Solve)