std::weak_ptr prevents circular reference leak

#include <iostream>
#include <memory>

struct Node {
    int val;
    std::shared_ptr<Node> next;
    // Shared pointer back to parent causes reference cycle
    std::shared_ptr<Node> prev;
    Node(int v) : val(v) {}
};

int validateNodeLinking(int val) {
    auto n1 = std::make_shared<Node>(1);
    auto n2 = std::make_shared<Node>(val);
    n1->next = n2;
    n2->prev = n1; // Cycle: n1 and n2 reference count never reaches 0!
    return n2->val;
}

int main() {
    std::cout << validateNodeLinking(7) << std::endl;
    return 0;
}