AlgoExpert Merge Overlapping Intervals

def mergeOverlappingIntervals(intervals):
    intervals.sort(key=lambda i:i[0])
    output = [intervals[0]]
    
    for start, end in intervals[1:]:
        lastend = output[-1][1]
        if start > lastend:
            output.append([start, end])
        else:
            output[-1][1] = max(end, lastend)
        
    return output