Odd Even Linked List LeetCode solution in C++

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class Solution {
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 public:
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  ListNode *oddEvenList(ListNode *head) {
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    if (head == NULL || head->next == NULL || head->next->next == NULL) {
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      return head;
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    }
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    ListNode *first = head;
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    ListNode *second = head->next;
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    ListNode *last = head;
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    int count = 1;
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    while (last->next != NULL) {
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      last = last->next;
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      count++;
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    }
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    int n = count / 2;
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    while (n != 0) {
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      first->next = second->next;
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      last->next = second;
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      second->next = NULL;
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      first = first->next;
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      last = second;
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      second = first->next;
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      n--;
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    }
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    return head;
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  }
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};