I was trying to solve this problem LISA Problem - CodeChef. This problem is unsolved till now. I wrote this O(NlogN) solution Ubuntu Pastebin but getting WA. I tested with many random inputs (of size <=10^4 by generating random numbers). To make sure that my code gives correct result for those random inputs I wrote another DP solution Ubuntu Pastebin and checked if outputs were identical. It matched in all cases i tested with (If my dp solution isn’t wrong) and couldn’t find any corner case too. Can anyone please provide a test case where my code fails?