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class Solution {
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 public:
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  ListNode *solve(ListNode *head, ListNode *temp) {
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    if (temp == NULL) return head;
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    ListNode *curr = solve(head, temp->next);
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    if (!curr) return NULL;
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    if (curr == temp) {
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      curr->next = NULL;
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      return nullptr;
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    }
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    if (curr->next == temp) {
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      temp->next = nullptr;
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      return NULL;
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    }
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    temp->next = curr->next;
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    curr->next = temp;
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    curr = temp->next;
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    return curr;
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  }
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  void reorderList(ListNode *head) {
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    solve(head, head);
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  }
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};