Solution.cpp

/*
// Definition for a Node.
class Node {
public:
    int val;
    Node* next;
    Node* random;
    
    Node(int _val) {
        val = _val;
        next = NULL;
        random = NULL;
    }
};
*/

class Solution {
public:
    Node* copyRandomList(Node* head) {
        if (!head) {
            return nullptr;
        }
        Node* cur = head;
        while (cur) {
            Node* node = new Node(cur->val);
            node->next = cur->next;
            cur->next = node;
            cur = node->next;
        }

        cur = head;
        while (cur) {
            cur->next->random = cur->random ? cur->random->next : nullptr;
            cur = cur->next->next;
        }

        Node* copy = head->next;
        cur = head;
        while (cur) {
            Node* next = cur->next;
            cur->next = next->next;
            next->next = next->next ? next->next->next : nullptr;
            cur = cur->next;
        }
        return copy;
    }
};