I was giving this round https://codeforces.net/contest/1542 and wasn't able to solve problem B. Though after just a small hint I was able to solve it but I can't get over the fact that I wasn't able to approach this question . are the some good resources for constructive algorithm questions or its just natural for some people ? if there are some good resources please do share them. It's not just the mentioned contest I want to improve ability to solve constructive algorithm questions in general.

thanks in advance