mode.cpp

#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>

template<typename I>
std::pair< typename std::iterator_traits<I>::value_type, size_t> mode(I start, I end) {       
    typedef typename std::iterator_traits<I>::value_type V;
    
    if (start == end) {
        return std::make_pair(V(), 0);   
    }

    std::vector< V > sorted;
    std::copy(start, end, std::back_inserter(sorted)); 
    std::sort(sorted.begin(), sorted.end());
    
    size_t best_len = 1;
    auto it = sorted.begin();
    auto best_group = it;
    auto group_start = it;
    ++it;
    
    while (it != sorted.end()) {
        if (*it != *group_start) {
            size_t len = it - group_start;
            if (len > best_len) {
                best_len = len;
                best_group = group_start;
            }
            group_start = it;
        }
        ++it;
    }
    
    return std::make_pair(*best_group, best_len);
}


int main()
{
    int test[] = { 1, 2, 3, 4, 4, 3, 4, 5, 6, 6 };
    auto item = mode(test, test + sizeof(test) / sizeof(int));
    std::cout << item.first << ", " << item.second <<std::endl;
    return 1;
}