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.

 

Solution: Solution 1 uses constant extra space.

/**
 * 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) return NULL;
        unordered_map<RandomListNode *, RandomListNode *> map;
        RandomListNode dummy(0), *curNew = &dummy, *cur = head;
        while (cur) 
        {
            if (map.find(cur) == map.end())
                map[cur] = new RandomListNode(cur->label);
            if (cur->random && map.find(cur->random) == map.end())
                map[cur->random] = new RandomListNode(cur->random->label);
            curNew->next = map[cur];
            curNew = curNew->next;
            curNew->random = map[cur->random];
            cur = cur->next;
        }
        return dummy.next;
    }
};