https://leetcode.cn/problems/merge-intervals/description/?envType=study-plan-v2&envId=top-interview-150

class Solution:
    def merge(self, intervals: List[List[int]]) -> List[List[int]]:
        ans=[]
        intervals.sort()
        for l, r in intervals:
            if not ans or ans[-1][1]<l:
                ans.append([l, r])
            else:#可以省略，但时间会小长
                ans[-1][1]=max(ans[-1][1], r)
        return ans