#include <algorithm>
#include <iostream>
#include <vector>
 
void displayFrequentNumber(const std::vector<int>& input)
{
    std::vector<std::pair<int, std::size_t>> v;
 
    for (std::size_t i = 0; i != input.size(); ++i) {
        v.push_back({input[i], i});
    }
    std::sort(begin(v), end(v));
    for (auto it = begin(v); it != end(v); ) {
        auto next = find_if(it, end(v),
                            [it](const std::pair<int, std::size_t>& rhs)
                                {return it->first != rhs.first;});
        if (next - it >= 3) {
            std::cout << it->first << ":";
            for (; it != next; ++it) {
                std::cout << " " << it->second;
            }
            std::cout << std::endl;
        }
        it = next;
    }
}
 
int main(int argc, char *argv[])
{
    displayFrequentNumber({6,4,4,5,2,4,4,3,5,5});
    return 0;
}
 

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