Find cycles, C++ (clang)

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//clang 3.8.0

#include <iostream>
#include <unordered_map>
#include <vector>

const auto M = []{
    std::unordered_map <int, std::vector <int> > M;
    M[1] = std::vector<int>{ 1, 8, 12, 7 };
    M[4] = std::vector<int>{ 4, 3, 5 };
    M[7] = std::vector<int>{ 7, 9, 13, 18, 0, 2 };
    M[2] = std::vector<int>{ 2, 11, 1 };
    M[5] = std::vector<int>{ 5, 17, 10, 4 };
    M[9] = std::vector<int>{ 9, 6, 19, 14 };
    M[14] = std::vector<int>{ 14, 15, 9 };
    return M;
}();

bool try_follow(int from, std::vector<int>& result)
{
    int current = from;
    while (true) {
        auto path = M.find(current);
        if (path == M.end()) return false;
        current = path->second.back();
        if (current < from) return false;
        result.insert(result.end(), path->second.begin()+1, path->second.end());
        if (current == from) return true;
    }
}

int main(void)  
{
    for( auto& kvp : M )
    {
        std::vector<int> x;
        if (try_follow(kvp.first, x)) {
            std::cout << kvp.first;
            for( int y : x )
                std::cout << " - " << y;
            std::cout << std::endl;
        }
    }
}

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Compilation time: 1.13 sec, absolute running time: 0.21 sec, cpu time: 0.15 sec, memory peak: 3 Mb, absolute service time: 1,34 sec