do we need to solve DP problems separately or just keep solving the problems in mixed pool and eventually everything will fall at its place

link to problem — (https://onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=1285) link to my code — (https://ideone.com/pAMZpL) i am getting WA and not able to figure out why? thank you

Here is my submission.can someone point out my mistake thanks in advance. link to my submission

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can somebody explain me the logic of problem E of abc 168.https://atcoder.jp/contests/abc168/tasks/abc168_e.i know that the points chosen according to given condition will form perpendicular lines but i am not able to proceed further.

HOW TO SOLVE THE INEQUALITY i*(i + 1) <= n such that i is maximum possible in O(1) time complexity.is their exist any method.

I am using 3 pointer technique to minimize the difference between largest and smallest element chosen and then finding the mid element which minimizes the answer. here is link to my code: https://ideone.com/XzeUzs thanks in advance