copy_list_with_random_pointer.cpp

// =====================================================================================
//
//       Filename:  copy_list_with_random_pointer.cpp
//
//    Description:  138. Copy List with Random Pointer.
//
//        Version:  1.0
//        Created:  09/10/2019 08:34:53 PM
//       Revision:  none
//       Compiler:  g++
//
//         Author:  Zhu Xianfeng (), xianfeng.zhu@gmail.com
//   Organization:  
//
// =====================================================================================
#include <stdio.h>

class Node
{
public:
    int val;
    Node* next;
    Node* random;

    Node() {}

    Node(int _val, Node* _next, Node* _random)
    {
        val = _val;
        next = _next;
        random = _random;
    }
};

class Solution
{
public:
    Node* copyRandomList(Node* head)
    {
        if (head == nullptr)
        {
            return nullptr;
        }

        int num = 0;
        Node* copy = nullptr;
        Node* ptr1 = head;
        Node* ptr2 = nullptr;
        Node* tail1 = nullptr;
        Node* tail2 = nullptr;

        // Copy linked list
        while (ptr1 != nullptr)
        {
            auto* node = new Node(ptr1->val, nullptr, nullptr);
            if (ptr2 == nullptr)
            {
                copy = node;
            }
            else
            {
                ptr2->next = node;
            }

            num++;
            ptr2 = node;
            tail1 = ptr1;
            tail2 = ptr2;
            ptr1 = ptr1->next;
        }

        // Link tail and head
        tail1->next = head;
        tail2->next = copy;

        // Copy random pointer
        ptr1 = head;
        ptr2 = copy;
        while (num > 0)
        {
            if (ptr1->random == nullptr)
            {
                ptr2->random = nullptr;
            }
            else
            {
                auto* p = ptr1;
                auto* q = ptr2;
                while (p != ptr1->random)
                {
                    p = p->next;
                    q = q->next;
                }

                // Found random
                ptr2->random = q;
            }

            ptr1 = ptr1->next;
            ptr2 = ptr2->next;
            num--;
        }

        // Unlink tail and head
        tail1->next = nullptr;
        tail2->next = nullptr;

        return copy;
    }
};

int main(int argc, char* argv[])
{
    Node* head = nullptr;
    Node* copy = Solution().copyRandomList(head);
    printf("Finish copy: %p\n", copy);
    return 0;
}