56. Merge Intervals

def merge(self, intervals):
        """
        :type intervals: List[Interval]
        :rtype: List[Interval]
        """
        res = []
        for i in sorted(intervals, key=lambda x: x.start):
            if res and i.start <= res[-1].end:
                res[-1].end = max(i.end, res[-1].end)
            else:
                res.append(i)
        return res