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impl Solution {
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  pub fn odd_even_list(head: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
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    let mut head = head;
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    let mut odd = Box::new(ListNode::new(-1));
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    let mut cur_odd = &mut odd;
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    let mut even = Box::new(ListNode::new(-1));
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    let mut cur_even = &mut even;
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    let mut is_odd = true;
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    while head.is_some() {
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      if is_odd {
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        cur_odd.next = head;
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        cur_odd = cur_odd.next.as_mut()?;
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        head = cur_odd.next.take();
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      } else {
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        cur_even.next = head;
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        cur_even = cur_even.next.as_mut()?;
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        head = cur_even.next.take();
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      }
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      is_odd = !is_odd;
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    }
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    cur_odd.next = even.next;
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    return odd.next;
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  }
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}