第二题AC代码 nums=[[4,1],[9,3],[5,5],[2,4],[2,1]] def solution(nums):     nums.sort(key=lambda x:(x[0],x[1]))     res=[nums[0]]     for num in nums[1:]:         found=False         for i in range(len(res)):             if num[0]>=res[i][0] and num[1]>=res[i][1]:                 res[i]=num                 found=True                 break         if found==False:             res.append(num)     return len(res) solution(nums)