Copy List with Random Pointer LeetCode solution in C++

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class Solution {
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 public:
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  Node *copyRandomList(Node *head) {
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    if (head == NULL) {
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      return NULL;
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    }
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    Node *temp = head;
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    while (temp != NULL) {
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      Node *m = new Node(temp->val);
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      m->next = temp->next;
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      temp->next = m;
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      temp = temp->next->next;
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    }
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    temp = head;
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    while (temp != NULL) {
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      if (temp->random == NULL) {
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        temp->next->random = NULL;
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      } else {
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        temp->next->random = temp->random->next;
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      }
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      temp = temp->next->next;
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    }
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    temp = head;
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    Node *p = new Node(-1);
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    Node *r = p;
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    Node *q = head;
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    while (q != NULL) {
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      q = q->next->next;
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      p->next = temp->next;
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      p = p->next;
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      temp->next = q;
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      temp = temp->next;
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    }
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    p->next = NULL;
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    return r->next;
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  }
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};