/*
VIM: let b:cf5build="clang -std=c++20 -O2 -pthread -lstdc++ -I. {SRC} -o {OUT}"
VIM: let b:cf5run="{OUT}"
*/
#include <iostream>
#include <exception>
#include <chrono>
#include <vector>

void print(const std::vector<int>& row)
{
    for (auto i : row){
        std::cout << i << ',';
    }
    std::cout << std::endl;
}

void print(const std::vector<std::vector<int>>& board)
{
    for (const auto& row : board){
        for (auto i : row){
            std::cout << i << ',';
        }
        std::cout << std::endl;
    }
}

struct OneDimVec
{
    using board_t = std::vector<int>;
    using iterator_t = int *;
    enum {dimentions=1};
    static iterator_t begin(board_t& b, int n){
        return b.data();
    }
    static iterator_t end(board_t& b, int n){
        return b.data()+b.size();
    }
    static iterator_t next(iterator_t it){
        return it+1;
    }
};

struct OneDimVecReverse
{
    using board_t = std::vector<int>;
    using iterator_t = board_t::reverse_iterator;
    enum {dimentions=1};
    static iterator_t begin(board_t& b, int n){
        return b.rbegin();
    }
    static iterator_t end(board_t& b, int n){
        return b.rend();
    }
    static iterator_t next(iterator_t it){
        return it+1;
    }
};


template <typename Traits>
void push(typename Traits::board_t& board, int n)
{
    auto q = Traits::begin(board, n);
    auto pe = Traits::end(board, n);
    for (auto p = Traits::next(q); p != pe; p=Traits::next(p)){
        if (*p==0){
            continue;
        }
        else if (*q == 0){
            *q+=*p;
            *p = 0;
        }
        else if (*q == *p){
            *q+=*p;
            *p = 0;
            q = Traits::next(q);
        }
        else {
            q = Traits::next(q);
            *q = *p;
            if (q != p){
                *p = 0;
            }
        }
    }
}

template <typename T>
void test(typename T::board_t v){
    std::cout << "--------------" << std::endl;
    print(v);
    if constexpr (T::dimentions == 1){
        push<T>(v,0);
    } else {
        for (int i = 0; i < T::dim_size(v); ++i){
            push<T>(v,i);
        }
    }
    std::cout << "-" << std::endl;
    print(v);
}

struct BoardTraits
{
    using board_t=std::vector<std::vector<int>>;
    enum {dimentions=2};
    struct iterator_t {
        board_t& b;
        int i;
        int j;
        int& operator*(){
            return b[i][j];
        }
        bool operator != (const iterator_t& it){
            return i != it.i;
        }
        iterator_t& operator = (const iterator_t& it){
            i=it.i;
            j=it.j;
            return *this;
        }
    };
};

struct Up : public BoardTraits
{
    static int dim_size(const board_t& b){
        return b[0].size();
    }
    static iterator_t begin(board_t& b, int n){
        return {b, 0, n};
    }
    static iterator_t end(board_t& b, int n){
        return {b, int(b.size()), n};
    }
    static iterator_t next(const iterator_t& it){
        return {it.b, it.i+1, it.j};
    }
};

struct Down : public BoardTraits
{
    static int dim_size(const board_t& b){
        return b[0].size();
    }
    static iterator_t begin(board_t& b, int n){
        return {b, int(b.size())-1, n};
    }
    static iterator_t end(board_t& b, int n){
        return {b, -1, n};
    }
    static iterator_t next(const iterator_t& it){
        return {it.b, it.i-1, it.j};
    }
};

struct Left : public BoardTraits
{
    using iterator_t = std::vector<int>::iterator;
    static int dim_size(const board_t& b){
        return b.size();
    }
    static iterator_t begin(board_t& b, int n){
        return b[n].begin();
    }
    static iterator_t end(board_t& b, int n){
        return b[n].end();
    }
    static iterator_t next(const iterator_t& it){
        return it+1;
    }
};

struct Right : public BoardTraits
{
    using iterator_t = std::vector<int>::reverse_iterator;
    static int dim_size(const board_t& b){
        return b.size();
    }
    static iterator_t begin(board_t& b, int n){
        return b[n].rbegin();
    }
    static iterator_t end(board_t& b, int n){
        return b[n].rend();
    }
    static iterator_t next(const iterator_t& it){
        return it+1;
    }
};


int main ( void )
{try{
    auto begin = std::chrono::high_resolution_clock::now();

    test<OneDimVec>({4, 0, 4, 8});
    test<OneDimVecReverse>({4, 0, 4, 8});
    std::cout << "test" << std::endl;
    //......
    test<Left>({
             {4, 0, 4, 8},
             {2, 0, 2, 8},
             {1, 1, 0, 0},
             {4, 0, 4, 4}
             });
    test<Right>({
             {4, 0, 4, 8},
             {2, 0, 2, 8},
             {1, 1, 0, 0},
             {4, 0, 4, 4}
             });
    test<Up>({
             {4, 0, 4, 8},
             {2, 0, 2, 8},
             {1, 1, 0, 0},
             {4, 0, 4, 4}
             });
    test<Down>({
             {4, 0, 4, 8},
             {2, 0, 2, 8},
             {1, 1, 0, 0},
             {4, 0, 4, 4}
             });

    auto end = std::chrono::high_resolution_clock::now();
    std::chrono::duration<double> seconds = end - begin;
    std::cout << "Time: " << seconds.count() << std::endl;
    return 0;
}
catch ( const std::exception& e )
{
    std::cerr << std::endl
            << "std::exception(\"" << e.what() << "\")." << std::endl;
    return 2;
}
catch ( ... )
{
    std::cerr  << std::endl
            << "unknown exception." << std::endl;
    return 1;
}}