#include // --- Helper classes // class used to store list of int that needs to be processed template struct Pack{}; // class used to store the result template struct ResPack{}; // Class that store a type (used for FindLeader) template struct Type{ using type = T; }; // Class that keeps a certain value of a certain type template struct Value{ const static T value = val; }; // boolean version of Value (BOOL == Value) template using BOOL = Value; // --- If class // generic declaration template struct IF{}; // specialization for A == true: keeping first type template struct IF : T {}; // specialization for A == false: keeping second type template struct IF : U {}; // --- IsLeader class // generic declaration template struct IsLeader : BOOL {}; // end point specialization which will be either transformed to BOOL or BOOL depending on the result of N < I template struct IsLeader > : IF<(N < I), BOOL, BOOL > {}; // specialization that will go through all parameters of the pack and if one of them is greater than N, IsLeader is transformed to BOOL, else I is removed from the Pack template struct IsLeader > : IF<(N < I), BOOL, IsLeader> > {}; // --- FindLeaders class // generic declaration template struct FindLeader{}; // specialization for the case where there is only one integer in the list or where only the last integer is a leader, transfert template parameter from Pack to ResPack template struct FindLeader> : FindLeader>{}; // specialization that is the starting point when there are multiple integers, if the first one is leader, it is kept in a ResPack, else it is removed template struct FindLeader> : IF< IsLeader>::value, FindLeader, Pack>, FindLeader> > {}; // specialization that represent one "iteration", if the first integer of the Pack is a leader, it is added to the ResPack, else it is removed template struct FindLeader, Pack> : IF< IsLeader>::value, FindLeader, Pack>, FindLeader, Pack> > {}; // specialization that is the stopping point when there is more than one leader, the last integer of the list is ALWAYS a leader template struct FindLeader, Pack> : FindLeader>{}; // specialization to transfert the ResPack from FindLeader class to Tyoe when all the list is_processed template struct FindLeader> : Type>{}; // helper to prevent having to write "typename FindLeader>::type" and instead write "findleader_t<...>" template using findleader_t = typename FindLeader>::type; // --- Class to display the result // generic declaration template struct Result{ Result(){ std::cout << "no result" << std::endl; } }; // specialization that display J and inherit from Result so that its constructor will be called and so on template struct Result : Result{ Result() : Result(){ std::cout << J << std::endl; } }; // specialization to stop the recursive inheritance and display the last integer template struct Result{ Result(){ std::cout << I << std::endl; } }; // --- Make result class // generic declaration template struct MakeRes{}; // specialization that remove the resulting list of int from ResPack to put it in Result to be shown template struct MakeRes> : Result{}; int main() { std::cout << "Leaders of [1, 2, 3, 4]" << std::endl; MakeRes>(); std::cout << "\nLeaders of [4, 3, 2, 1]" << std::endl; MakeRes>(); std::cout << "\nLeaders of [1, 4, 2, 3]" << std::endl; MakeRes>(); return 0; }

sayan challenge: leader finder