题目
Given a list of intervals, remove all intervals that are covered by another interval in the list.
Interval [a,b) is covered by interval [c,d) if and only if c <= a and b <= d.
After doing so, return the number of remaining intervals.
解题思路
先对所有区间进行排序，左端点从小到大，右端点从大到小，然后遍历每个区间，如果新的区间不被之前的包含，结果+1
代码
class Solution:
def removeCoveredIntervals(self, intervals: List[List[int]]) -> int:
intervals.sort(key = lambda x: (x[0], -x[1]))
res = prev = 0
for _, r in intervals:
if r > prev:
res += 1
prev = r
return res
