Copy List with Random Pointer （Hash表）

class Solution {
public:
    RandomListNode *copyRandomList(RandomListNode *head) {
        if(head==NULL) return head;
        map<RandomListNode*,int> hash;
        map<int,RandomListNode*> copyHash;

        RandomListNode* copyHead=new RandomListNode(head->label);
        RandomListNode* p=head;
        RandomListNode* q=copyHead;
        int index=0;
        hash[p]=index;
        copyHash[index]=q;
        ++index;
        p=p->next;

        //复制整个链表
        while(p!=NULL){
            RandomListNode* newNode=new RandomListNode(p->label);
            q->next=newNode;
            q=q->next;
            hash[p]=index;
            copyHash[index]=q;
            ++index;
            p=p->next;
        }
        //最后的NULL节点也要加进去
        hash[NULL]=index;
        copyHash[index]=NULL;
        
        //复制random指针
        int i=0;
        RandomListNode* r=head;
        while (i<hash.size()&&r!=NULL)
        {
            copyHash[i]->random=copyHash[hash[r->random]];
            ++i;
            r=r->next;
        }
        return copyHead;
    }
};