#include <iostream>
#include <memory>
#include <utility>

class Node {
public:
    Node(const int value, std::unique_ptr<Node> next)
        : next_(std::move(next)), value_(value) {}

    explicit Node(const int v)
        : Node(v, nullptr) {}

    const Node* next() const { return next_.get(); }
    int value() const { return value_; }
    std::unique_ptr<Node> getNext() { return std::move(next_); }

private:
    std::unique_ptr<Node> next_;
    int value_;
};

// 1
// 2 -> 1
// 3 -> 2 -> 1
// 4 -> 3 -> 2 -> 1

class List {
public:
    void pushFront(int value) {
        if (!head_) {
            head_ = std::make_unique<Node>(value);
            return;
        }

        head_ = std::make_unique<Node>(value, std::move(head_));
    }

    const Node* findByValue(const int value) const {
        const auto* current = head_.get();

        while (current) {
            if (current->value() == value) {
                return current;
            }
            current = current->next();
        }

        return nullptr;
    }

private:
    std::unique_ptr<Node> head_;
};

int main() {
    List list;

    list.pushFront(4);
    list.pushFront(2);
    list.pushFront(7);
    list.pushFront(9);

    if (const auto* const node = list.findByValue(1)) {
        std::cout << node->value() << '\n';
    } else {
        std::cout << "can't find node with value 1\n";
    }

    if (const auto* const node = list.findByValue(7)) {
        std::cout << node->value() << '\n';
    } else {
        std::cout << "can't find node with value 7\n";
    }

    return 0;
}