frequency.cc

#include <map>
#include <tuple>
#include <vector>
#include <iostream>
#include <algorithm>

template<typename KeyType>
std::pair<KeyType, std::size_t> most_frequent_element(std::vector<KeyType> elts) {
    std::map<KeyType, std::size_t> frequency_table;
 
    auto pair_second_less_than = [](std::pair<KeyType const, std::size_t> const& a,
                                    std::pair<KeyType const, std::size_t> const& b) {
        return a.second < b.second;
    };

    for (auto i : elts) {
            frequency_table[i]++;
    }

    return  *std::max_element(frequency_table.begin(),
                              frequency_table.end(),
                              pair_second_less_than);
}

int main() {
    std::vector<int> test = {1,2,3,4,5,6,3,3,3,3,3,5,5,5,5,5,5,5,5,5,6,7,7,8,3,3,1984};
    std::pair<int, std::size_t> entry = most_frequent_element(test);
    std::cout << "(" << entry.first << " " << entry.second << ")" << std::endl;
    return 0;
}

/*

clang++ frequency.cc -Wall -Werror -pedantic -std=c++11  

~/code/exercises/misc/element-frequencies $ ./a.out 
(5 10)

*/