[LeetCode] Copy List with Random Pointer

Analysis

Apparently, it’s not a difficult question to clone a linked list without an additional random pointer. For us, the trickier part, however, is to clone the random list node structure. My idea is using a HashTable.

Code

/**
* Author : Acjx
* Email  : zhoujx0219@163.com
*/

/**
* 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:
/**
* @param head: The head of linked list with a random pointer.
* @return: A new head of a deep copy of the list.
*/
RandomListNode *copyRandomList(RandomListNode *head)
{
RandomListNode *dummyHead = new RandomListNode(0);
RandomListNode *p = head, *q = dummyHead;
unordered_map<RandomListNode *, RandomListNode *> map;

while (p != NULL)
{
q->next = new RandomListNode(p->label);
map.insert(make_pair(p, q->next));
p = p->next;
q = q->next;
}

p = head; q = dummyHead;
while (p != NULL)
{
q->next->random = map[p->random];
p = p->next;
q = q->next;
}

return dummyHead->next;
}
};