Copy list with random pointer

/**
 * 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 NULL;
        RandomListNode *result = new RandomListNode(head->label), *next, *random;
        
        unordered_map<RandomListNode*, RandomListNode*> dict;
        dict[head] = result;
        
        while (head){
            
            if (head->random){
                
                if (dict[head->random]) dict[head]->random = dict[head->random];
                else{
                    dict[head->random] = new RandomListNode(head->random->label);
                    dict[head]->random = dict[head->random];
                }
            }
            
            if (head->next){
                
                if (dict[head->next]) dict[head]->next = dict[head->next];
                else{
                    dict[head->next] = new RandomListNode(head->next->label);
                    dict[head]->next = dict[head->next];
                }
            }
            head = head->next;
        }
        return result;
    }
};