Leetcode: Copy List with Random Pointer

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.

分析：因为有random pointer，我们需要保存原结点对应的新结点来完成deep copy。时间复杂度为O(n), 空间复杂度为O(n)。

class Solution {
public:
    RandomListNode *copyRandomList(RandomListNode *head) {
        if(head == NULL) return NULL;
        unordered_map<RandomListNode *, RandomListNode *> pmap;
        
        for(RandomListNode *p = head; p; p = p->next){
            RandomListNode * q = new RandomListNode(p->label);
            pmap[p] = q;
        }
        
        for(RandomListNode *p = head; p; p = p->next){
            if(p->next)
                pmap[p]->next = pmap[p->next];
            if(p->random)
                pmap[p]->random = pmap[p->random];
        }
        
        return pmap[head];
    }
};