Question: https://algo.monster/problems/amazon_oa_num_ways_to_split_into_primes

Can anyone tell me how to approach this question. I feel lost

Question here:

https://atcoder.jp/contests/abc239/tasks/abc239_d

The question for the limits is brute but what is the approach if all a,b,c,d can be upto 10**5. I could not figure anything out on that case. Please help me

I'm still a beginner and I wanted questions where you would store some information of arrays or maybe strings in hashmaps to improve the codes time complexity. Can any of you please recommend me some questions? Thank you

Can anyone help me understand how to approach TSP problems like this one: https://leetcode.com/problems/shortest-path-visiting-all-nodes/description/

Just as the title says. Can anyone please provide sites similar to codeforces, SPOJ, codechef, atcoder, etc but for software development instead. Basically a lot of questions and topics to practice for.