t1.hpp

#include <string>
#include <set>
#include <vector>
// #include <map>
#include <unordered_map>
#include <queue>
#include<stdexcept>
#include <algorithm>


#ifndef Q1_HPP
#define Q1_HPP

namespace q1 {
    class neighbour {
        public:
            explicit neighbour(std::size_t rung_distance = 1);
            neighbour(const neighbour &other) = default;
            neighbour(neighbour &&other) noexcept = default;
            virtual ~neighbour() noexcept = default;
            // auto operator=(const neighbour &other) = default;       // 1
            // auto operator=(neighbour &&other) noexcept = default;   // 2
            auto get_rung() const noexcept -> std::size_t;
            virtual auto get_neighbours(const std::string &curr, const std::set<std::string> &lexicon) const -> std::set<std::string>;
        private:
            auto check(std::string a,std::string b) const -> bool;
            std::size_t rung_distance_;
    };

    auto generate(
        const std::string &start,
        const std::string &end,
        const std::set<std::string> &lexicon,
        const neighbour &strategy
    ) -> std::vector<std::string>;




} // namespace q1

#endif // Q1_HPP

t1.cpp

#include <q1/q1.hpp>

namespace q1 {
    auto generate(
        const std::string &start,
        const std::string &end,
        const std::set<std::string> &lexicon,
        const neighbour &strategy
    ) -> std::vector<std::string> {
        if (start.size() != end.size()) {
            return {};
        }
        
        std::unordered_map<std::string, std::set<std::string>> vis;
        std::queue<std::string> q;
        std::unordered_map<std::string, std::string> pa;
        while (!q.empty()) {
            int size = q.size();
            while (size--) {
                auto f = q.front(); q.pop();
                if (!vis.count(f)) {
                    vis[f] = strategy.get_neighbours(f, lexicon);
                }
                auto& neibor = vis[f];
                for (auto& p : neibor) {
                    if (!pa.count(p)) pa[p] = f;
                    if (!vis.count(p)) {
                        q.push(p);
                    }
                }
            }
        }
        bool ok = 1;
        std::string cur = end;
        std::vector<std::string> ans;
        ans.push_back(end);
        while (cur != start) {
            if (!pa.count(cur)) {
                ok = 0; break;
            }
            cur = pa[cur];
            ans.push_back(cur);
        }
        std::reverse(ans.begin(), ans.end());
        if (!ok) return {};
        else return ans;
    }

    neighbour::neighbour(std::size_t rung_distance){
        if (rung_distance == 0){
            throw std::domain_error("rung_distance is zero");
        }
        rung_distance_ = rung_distance;
    }

    auto neighbour::get_rung() const noexcept -> std::size_t{
        return rung_distance_;
    }

    auto neighbour::check(std::string a,std::string b) const -> bool{
        if( a.size() != b.size() ) return false;
        int count = 0;
        for(int i = 0 ; i< a.size();i++){
            if(a[i]!=b[i]) count++;
        }
        return count==rung_distance_;
    }
    auto neighbour::get_neighbours(const std::string &curr, const std::set<std::string> &lexicon) const -> std::set<std::string>{
        std::set<std::string> res{};
        for( auto const& word:lexicon){
            if ( check(curr,word) )
            {
                res.insert(word);
            }
        }
        return res;
    }

} // namespace q1

## T2

t2.hpp

#include <type_traits>
#include <stdexcept>


#ifndef Q2_HPP
#define Q2_HPP

namespace q2 {
    template <typename T>
    struct remove_array_ref
    {
        using type = typename std::remove_all_extents<typename std::remove_reference<T>::type>::type ;
    };

    template <typename T>
    using remove_array_ref_t = typename remove_array_ref<T>::type;

    template <typename T, auto N>
    class sso_optional {
    public:
        using value_type = remove_array_ref_t<T>;
        using reference = value_type&;
        using pointer = std::conditional<std::is_class<value_type>::value, value_type*, void>;
        // std::enable_if<std::is_class<value_type>::value>
        // using pointer = value_type*;

        // std::enable_if<!std::is_class<value_type>::value>
        // using pointer = typename nullptr;
        T value;
        sso_optional() noexcept {
            // static_cast<reference>(*this) = N;
            value = N;
        }
        
        explicit sso_optional(const value_type &arg) noexcept {
            value = value_type(arg);
        }

        template<typename ...Args>
        explicit sso_optional(Args&& ...args) noexcept {
            value = value_type(std::forward<Args>(args)...);
        }

        sso_optional(const sso_optional &other) = delete;       // 4
        
        sso_optional(sso_optional &&other) noexcept {
            value = move(other);
            other = N;
        }

        ~sso_optional() noexcept {
            if (bool(value)) {
                if (!std::is_same<pointer, void>::value) {
                    // delete static_cast<pointer>(value);
                }
            }
        }

        auto operator=(const sso_optional &other) -> sso_optional& = delete;  // 1

        auto operator=(sso_optional &&other) noexcept -> sso_optional& {
            if (this == &other) return static_cast<reference>(*this); // self
            if (bool(value) && !std::is_same<pointer, void>::value) {
                delete static_cast<pointer>(value);
            }
            value = move(other);
            other = N;
        }

        operator bool() const noexcept {
            return static_cast<value_type>(value) != N;
        }


        auto operator*() -> reference {
            if (value != N) {
                return static_cast<reference>(value);
            } else {
                throw std::runtime_error();
            }
        }
        auto operator->() -> pointer {
            if (value != N) {
                return static_cast<pointer>(value);
            } else {
                throw std::runtime_error();
            }
        }

        auto operator==(const sso_optional &other) const noexcept -> bool {
            if (value == N && other == N || (value != N && other != N && value == other)) {
                return true;
            } else {
                return false;
            }
        }
    };
    
}

#endif // Q2_HPP

t2.cpp

q2.hpp__

#ifndef Q2_HPP
#define Q2_HPP

#include <type_traits>

namespace q2 {

    #define SSO_MOV(x) static_cast<std::remove_reference_t<decltype(x)>&&>(x)
    #define SSO_FWD(x) static_cast<decltype(x)&&>(x)

    template <typename T>
    struct remove_array_ref
    {
        using type = typename std::remove_all_extents<typename std::remove_reference<T>::type>::type ;
    };

    template <typename T>
    using remove_array_ref_t = typename remove_array_ref<T>::type;

    template <typename T, auto N>
    class sso_optional {

        constexpr void maybe_init_union(){
            if (std::is_constant_evaluated())
                dummy = N;
        }

    public:
        using value_type = remove_array_ref_t<T>;
        using reference = value_type &;
        using pointer = std::conditional<std::is_class<value_type>::value, value_type*, void>;

        sso_optional() noexcept;
        explicit sso_optional(const value_type &arg) noexcept;
        template<typename ...Args>
        explicit sso_optional(Args&& ...args) noexcept;
        sso_optional(const sso_optional &other) = delete;
        sso_optional(sso_optional &&other) noexcept;

        ~sso_optional()
        {
            if (!_state)
                return;
            value_.~T();
        }

        constexpr void reset_no_check(){
            if constexpr (not std::is_trivially_destructible_v<T>){
                value_.~T();
            }
            _state = false;
        }

        constexpr bool has_value() const noexcept {
            return this->_state;
        }

        union {
            char dummy;
            T value_;
        };

        bool _state;

        // assign
        auto operator=(const sso_optional &other) -> sso_optional& = delete;
        auto operator=(sso_optional &&other) noexcept -> sso_optional&;
        // bool
        operator bool() const noexcept;

        auto operator*() -> reference;   // 1
        auto operator->() -> pointer;    // 2

        auto operator==(const sso_optional &other) const noexcept -> bool;
    private:

        template <class sso_optional>
        constexpr auto& assign_from_optional(sso_optional&& o){
            switch( char(_state) + char(o.has_value()) * 2 ){
                case 0 :
                    break;
                case 1 :
                    this->reset_no_check();
                    break;
                case 2 :
                    this->construct_from(*SSO_FWD(o));
                    break;
                case 3 :
                    **this = *SSO_FWD(o);
                    break;
            }
            return *this;
        }

        template <class... Args>
        constexpr void construct_from(Args&&... args){
            std::construct_at(std::addressof(value_), static_cast<Args&&>(args)...);
            _state = true;
        }

        template <class sso_optional>
        constexpr void construct_from_optional(sso_optional&& opt){
            if (_state)
                this->construct_from(*SWL_FWD(opt));
            else
                this->maybe_init_union();
        }

        T* ptr(){ return std::addressof(value_); }
        const T* ptr() const { return std::addressof(value_); }
    };

    template<typename T, auto N>
    sso_optional<T, N>::sso_optional() noexcept {
        _state = false;
        dummy = N;
    }

    template<typename T, auto N>
    sso_optional<T, N>::sso_optional(const value_type &arg) noexcept {
        construct_from_optional(arg);
        _state = arg._state;
    }

    template<typename T, auto N>
    template<typename... Args>
    sso_optional<T, N>::sso_optional(Args &&... args) noexcept {
        this->construct_from(SSO_FWD(args)...);
        _state = true;
    }

    template<typename T, auto N>
    sso_optional<T, N>::sso_optional(sso_optional &&other) noexcept {
        this->construct_from_optional(SSO_FWD(other));
        _state = other.has_value();
    }

    template<typename T, auto N>
    auto sso_optional<T, N>::operator=(sso_optional &&other) noexcept -> sso_optional & {
        return this->assign_from_optional(SSO_FWD(other));
    }

    template<typename T, auto N>
    sso_optional<T, N>::operator bool() const noexcept {
        return has_value();
    }

    template<typename T, auto N>
    auto sso_optional<T, N>::operator*() -> reference {

        if(_state)
        {
            return value_;
        }
        else
        {
            throw std::runtime_error("1");
        }
    }

    template<typename T, auto N>
    auto sso_optional<T, N>::operator->() -> std::conditional<std::is_class<value_type>::value, value_type*, void> {

        if(!_state || typeid(pointer) == typeid(void))
        {
            throw std::runtime_error("2");
        }

        return this->ptr();
    }

    template<typename T, auto N>
    auto sso_optional<T, N>::operator==(const sso_optional &other) const noexcept -> bool {
        if (this->has_value() != other.has_value())
            return false;
        if (not this->has_value())
            return true;
        return *this == *other;
    }

}

#endif // Q2_HPP

q2.hpp:12:37: error: expected nested-name-specifier before ‘remove_array_ref_t’
   12 |         using value_type = typename remove_array_ref_t<T>;
      |                                     ^~~~~~~~~~~~~~~~~~
q2.hpp:13:36: error: expected nested-name-specifier before ‘value_type’
   13 |         using reference = typename value_type&;
      |                                    ^~~~~~~~~~
q2.hpp:16:34: error: expected nested-name-specifier before ‘value_type’
   16 |         using pointer = typename value_type*;
      |                                  ^~~~~~~~~~
q2.hpp:25:37: error: ‘value_type’ does not name a type
   25 |         explicit sso_optional(const value_type &arg) noexcept {
      |                                     ^~~~~~~~~~
q2.hpp:65:29: error: ‘reference’ does not name a type
   65 |         auto operator*() -> reference {
      |                             ^~~~~~~~~
q2.hpp:72:30: error: ‘pointer’ does not name a type
   72 |         auto operator->() -> pointer {
      |                              ^~~~~~~
q2.hpp: In constructor ‘q2::sso_optional<T, N>::sso_optional()’:
q2.hpp:22:25: error: ‘value_type’ does not name a type
   22 |             static_cast<value_type>(*this) = N;
      |                         ^~~~~~~~~~
q2.hpp: In constructor ‘q2::sso_optional<T, N>::sso_optional(const int&)’:
q2.hpp:26:25: error: ‘value_type’ does not name a type
   26 |             static_cast<value_type>(*this) = value_type(arg);
      |                         ^~~~~~~~~~
q2.hpp:26:46: error: there are no arguments to ‘value_type’ that depend on a template parameter, so a declaration of ‘value_type’ must be available [-fpermissive]
   26 |             static_cast<value_type>(*this) = value_type(arg);
      |                                              ^~~~~~~~~~
q2.hpp:26:46: note: (if you use ‘-fpermissive’, G++ will accept your code, but allowing the use of an undeclared name is deprecated)
q2.hpp: In constructor ‘q2::sso_optional<T, N>::sso_optional(q2::sso_optional<T, N>&&)’:
q2.hpp:37:25: error: ‘value_type’ does not name a type
   37 |             static_cast<value_type>(*this) = move(other);
      |                         ^~~~~~~~~~
q2.hpp: In destructor ‘q2::sso_optional<T, N>::~sso_optional()’:
q2.hpp:42:34: error: ‘value_type’ was not declared in this scope
   42 |             if (bool(static_cast<value_type>(*this))) {
      |                                  ^~~~~~~~~~
q2.hpp:42:17: error: expected primary-expression before ‘bool’
   42 |             if (bool(static_cast<value_type>(*this))) {
      |                 ^~~~
q2.hpp:42:17: error: expected ‘)’ before ‘bool’
q2.hpp:42:16: note: to match this ‘(’
   42 |             if (bool(static_cast<value_type>(*this))) {
      |                ^
q2.hpp:43:35: error: ‘pointer’ was not declared in this scope
   43 |                 if (!std::is_same<pointer, nullptr>::value) {
      |                                   ^~~~~~~
q2.hpp:43:51: error: template argument 1 is invalid
   43 |                 if (!std::is_same<pointer, nullptr>::value) {
      |                                                   ^
q2.hpp:43:51: error: type/value mismatch at argument 2 in template parameter list for ‘template<class, class> struct std::is_same’
q2.hpp:43:51: note:   expected a type, got ‘nullptr’
q2.hpp:44:40: error: ‘value_type’ does not name a type
   44 |                     delete static_cast<value_type>(*this);
      |                                        ^~~~~~~~~~
q2.hpp: In member function ‘q2::sso_optional<T, N>& q2::sso_optional<T, N>::operator=(q2::sso_optional<T, N>&&)’:
q2.hpp:52:52: error: ‘reference’ does not name a type
   52 |             if (this == &other) return static_cast<reference>(*this); // self
      |                                                    ^~~~~~~~~
q2.hpp:53:34: error: ‘value_type’ was not declared in this scope
   53 |             if (bool(static_cast<value_type>(*this)) && !std::is_same<pointer, nullptr>::value) {
      |                                  ^~~~~~~~~~
q2.hpp:53:17: error: expected primary-expression before ‘bool’
   53 |             if (bool(static_cast<value_type>(*this)) && !std::is_same<pointer, nullptr>::value) {
      |                 ^~~~
q2.hpp:53:17: error: expected ‘)’ before ‘bool’
q2.hpp:53:16: note: to match this ‘(’
   53 |             if (bool(static_cast<value_type>(*this)) && !std::is_same<pointer, nullptr>::value) {
      |                ^
q2.hpp:54:36: error: ‘value_type’ does not name a type
   54 |                 delete static_cast<value_type>(*this);
      |                                    ^~~~~~~~~~
q2.hpp:56:25: error: ‘value_type’ does not name a type
   56 |             static_cast<value_type>(*this) = move(other);
      |                         ^~~~~~~~~~
q2.hpp: In member function ‘q2::sso_optional<T, N>::operator bool() const’:
q2.hpp:61:32: error: ‘value_type’ does not name a type
   61 |             return static_cast<value_type>(*this) != N;
      |                                ^~~~~~~~~~
q2.hpp: In member function ‘bool q2::sso_optional<T, N>::operator==(const q2::sso_optional<T, N>&) const’:
q2.hpp:81:29: error: ‘value_type’ does not name a type
   81 |             if (static_cast<value_type>(*this) == N && other == N || (static_cast<value_type>(*this) != N && other != N && static_cast<value_type>(*this) == other)) {
      |                             ^~~~~~~~~~
q2.hpp:81:83: error: ‘value_type’ does not name a type
   81 |             if (static_cast<value_type>(*this) == N && other == N || (static_cast<value_type>(*this) != N && other != N && static_cast<value_type>(*this) == other)) {
      |                                                                                   ^~~~~~~~~~
q2.hpp:81:136: error: ‘value_type’ does not name a type
   81 |             if (static_cast<value_type>(*this) == N && other == N || (static_cast<value_type>(*this) != N && other != N && static_cast<value_type>(*this) == other)) {
      |