56.py

def merge(intervals: list[list[int]]) -> list[list[int]]:
    intervals.sort(key=lambda interval: interval[0])
    merged = []
    for interval in intervals:
        if not merged or merged[-1][1] < interval[0]:
            merged.append(interval)
        else:
            merged[-1] = [merged[-1][0], max(merged[-1][1], interval[1])]

    return merged


print(merge(intervals=[[1, 3], [2, 6], [8, 10], [15, 18]]))