Copy List with Random Pointer

 

    RandomListNode *copyRandomList(RandomListNode *head) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        //three steps
//1. 为原链表中每个节点创建一个shallow copy，用next指针指向这个copy节点。
//2. 利用原链表的next指针，将新链表的random指针指向正确的节点。
//3. 将两个链表分开。
        if(!head)
            return NULL;
        RandomListNode* cur = head,*next;
        RandomListNode* copy;
        // 1. 
        while(cur)
        {
            next = cur->next;
            copy = new RandomListNode(cur->label);
            cur->next = copy;
            copy->next = next;
            cur = next;
        }
        //2. 
        cur = head;
        while(cur)
        {

            copy = cur->next;
            if(cur->random)
                copy->random = cur->random->next;
            cur = copy->next;
        }
        
        //3. 
        RandomListNode* newHead = head->next;
        copy = newHead;
        head->next = copy->next;
        cur = copy->next;
        
        while(cur)
        {
            copy->next = cur->next;
            copy = copy->next;
            cur->next = copy->next;
            cur = cur->next;
        }
        return newHead;
        
    }