leetcode copy list with random pointer

不太熟练，拖了几天终于AC了。不过空间复杂度略高。。

struct RandomListNode {
	     int label;
	     RandomListNode *next, *random;
	     RandomListNode(int x) : label(x), next(NULL), random(NULL) {}
	 };

RandomListNode *copyRandomList(RandomListNode *head) {
	RandomListNode *cp = NULL;
	vector<int> labs;
	vector<RandomListNode *> randList;
	if(!head)return cp;
	labs.push_back(head->label);
	head->label = 0;
	cp = new RandomListNode(0);
	int i = 0;
	RandomListNode *pcp=cp, *phead=head;

	//tag nodes
	while(phead->next){
		i++;
		RandomListNode *newcp = new RandomListNode(i);
		
		labs.push_back(phead->next->label);
		pcp->next = newcp;
		phead->next->label= i;
		
		phead = phead->next;
		randList.push_back(pcp);
		pcp = newcp;
	}
	randList.push_back(pcp);
	//set random points
	pcp = cp;
	phead = head;
	RandomListNode *tmp = cp;
	i = 0;
	while(phead){
		if(phead->random){
			pcp->random = randList[phead->random->label];
		}
		phead = phead->next;
		pcp = pcp->next;
		i++;
	}

	//reset labels  
	i = 0;
	pcp = cp;
	phead = head;
	while(phead){
		phead->label = labs[i];
		pcp->label = labs[i];

		phead = phead->next;
		pcp = pcp->next;
		i++;
	}

	return cp;
}

leetcode上也有一些非常取巧的办法，比如利用指针地址都是连续的，然后取新链表和原链表的地址差，从而可以快速深拷贝，空间复杂度还很低：

RandomListNode *copyRandomList(RandomListNode *head) {
    if(head == NULL) return NULL;
    RandomListNode *newHead = new RandomListNode(head->label);
    newHead->random = head->random;
    head->label = newHead - head;

    RandomListNode *p = head->next, *q = newHead, *t;
    while(p) {
        t = new RandomListNode(p->label);
        t->random = p->random;
        p->label = t - p;
        q->next = t;
        q = t;
        p = p->next;
    }

    q = newHead;
    while(q) {
        if(q->random)
            q->random = q->random + q->random->label;
        q = q->next;
    }

    p = head;
    q = newHead;
    while(p) {
        p->label = q->label;
        p = p->next;
        q = q->next;
    }
    return newHead;
}

当然最厉害的还是重合的思想，都是奇思妙想啊：

RandomListNode *copyRandomList(RandomListNode *head) {
    if(head == NULL) return NULL;
    RandomListNode *p = head;
    do {
        RandomListNode *q = p->next;
        p->next = new RandomListNode(p->label);
        p->next->next = q;
        p = q;
    } while(p != NULL);
    p = head;
    do {
        p->next->random = (p->random == NULL) ? NULL : p->random->next;
        p = p->next->next;
    } while(p != NULL);
    p = head;
    RandomListNode *r = head->next;
    for(RandomListNode *q = r;;) {
        p->next = q->next;
        p = p->next;
        if(p == NULL) break;
        q->next = p->next;
        q = q->next;
    }
    return r;
}