TournamentSelection.h

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#ifndef TOURNAMENT_SELECTION_H
#define TOURNAMENT_SELECTION_H
 
#pragma once
 
#include "Selection.h"
#include <random>
#include <algorithm>
#include <stdexcept>
#include <cstddef>
 
namespace galib {
 
    template <typename GeneType>
    class TournamentSelection : public Selection<GeneType> {
    private:
        std::size_t tournament_size_m;
    public:
        explicit TournamentSelection(size_t tournament_size) : tournament_size_m(tournament_size) {
            if (tournament_size_m == 0) {
                throw std::invalid_argument("Tournament size must be at least 1.");
            }
        }
 
        std::size_t getTournamentSize() const { return tournament_size_m; }
 
        const Individual<GeneType>& select(const Population<GeneType>& population) override {
 
            thread_local static std::random_device rd;
            thread_local static std::mt19937 gen(rd());
 
            std::size_t pop_size = population.size();
            std::uniform_int_distribution<std::size_t> distribution(0, pop_size - 1);
 
            const Individual<GeneType>* winner = &population[distribution(gen)];
 
            for (std::size_t i = 1; i < tournament_size_m; ++i) {
                const Individual<GeneType>& candidate = population[distribution(gen)];
 
                if (candidate.getFitness() < winner->getFitness()) {
                    winner = &candidate;
                }
            }
            return *winner;
        }
    };
 
}
 
#endif // TOURNAMENT_SELECTION_H