Copy List with Random Pointer

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本文介绍了一种复杂链表结构的深拷贝方法，该链表除了常规的next指针外还包含了一个指向任意节点的随机指针。通过一种特殊的Z字形连接技巧，文章详细阐述了如何高效地完成链表的复制过程。

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A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.

Return a deep copy of the list.

很经典的一道题。先将新旧链表按Z字形连起来，再更新新链表的random指针，最后拆分新旧链表。

/**
 * Definition for singly-linked list with a random pointer.
 * struct RandomListNode {
 *     int label;
 *     RandomListNode *next, *random;
 *     RandomListNode(int x) : label(x), next(NULL), random(NULL) {}
 * };
 */
class Solution {
public:
    RandomListNode *copyRandomList(RandomListNode *head) {
        if(head==NULL) return head;
        RandomListNode *new_head = new RandomListNode(head->label);
        new_head->random = head->random;
        //combine list
        RandomListNode *p = head,*q = p->next,*r = new_head;
        p->next = new_head; 
        while(q){
            r->next = q;
            p = q->next;
            q->next = new RandomListNode(q->label);
            r = q->next;
            r->random = q->random;
            q = p;
        }
        
        r->next = NULL;
        p = new_head;
        while(p->next){ if(p->random) p->random = p->random->next; p = p->next->next; }
        if(p->random) p->random = p->random->next;  //the last node
        p = head;
        //split list
        while(p->next->next){
            q = p->next;
            p->next = q->next;
            q->next = p->next->next;
            p = p->next;
            q = q->next;
        }
       
        p->next = NULL;
        return new_head;
    }
};