Recently i tried my hands on this problem. I solved it using segment tree and fenwick tree but i don't know how to solve it using LIS concept. It would be very nice if some of you can share your approach for solving this.
Here is what i think regarding this!
We maintain a multiset and go on inserting elements from left to right adding elements one by one , finding the upper_bound of ai and removing it if its exists and then doing ans=max(ans,*st.rbegin()) if the size of my multiset is bigger than l.But this is giving me WA.I don't know where am i going wrong.It would be very helpful if someone can point out my mistake.