is there some sheet or website like a2oj ladders for codechef pratice problems ??

You can check out these learning paths for curated problems - Level up in DSA courses - CodeChef Learn

Thank you

What are topics required to solve the 5th problem in the div4 contest and how should one approach the question in the contest?

In the last 4 contests in 3 i was able to solve 4 problems in 40-45 min and sat for the remaining time thinking but was not able to come up with a solution to the fifth one.

what should i do ???

Firstly keep the goal clear: Being able to solve 5th problem in Div 4.

One way to achieve this is to attempt 5th problem every time and if you are not able to solve it, then look at the solution. Deeply understand the solution and implement it yourself. If you find that the solution uses some topic or concept which you donâ€™t know, learn that topic and solve more problems of that topic from practice.

Keep doing this for all future contests. On non-contest days as well, do the same thing for past contests. Open any past Div 4 contest and do the above steps for 5th problem of those contests. With enough consistency, you will be able to solve 5th problem in contest.