Algebra Score, how to solve?

general
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1

Problem link: https://www.codechef.com/PROC2018/problems/PROC18D
What should be the approach this question? Can’t we use stack in this?
I am not able to understand DP used in submitted solutions,how can we use DP in this question.

2

See this for Explanation : LINK

3

someOne help, please give any testcase where my code is failing
my code link