I participated in 4-5 long contest out of which in previous few contest i found that problems except challenge problem (top 4-5 easiest or more) can be solved using trees, graphs, dp, greedy, combinatorics, etc – etc, but whenever i look Challenge problem editorials and solutions it seems that there is something new here.
In November Contest in the editorial of problem SPELL, @dpraveen (Tester and Editorialist of problem SPELL) mentioned that @mugurelionut applied N-gram model, other top rankers used Trie,
In December Challenge in the editorial of Problem KALKI it was mentioned that prerequisites are Graph, Trees, Approximation, Ad-Hoc radio networks,
being a novice i really don’t know about trie or radio networks, etc.
SO could anyone please mention some suggested readings and basic algorithms for such kind of problems so that at least i as novice can learn them from low level and try to implement it…!