1
impl Solution {
2
  pub fn reverse_even_length_groups(head: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
3
    let mut head = head;
4
    let mut data = vec![];
5
    let mut ret = None;
6
    let mut tail = &mut ret;
7
    let mut sz = 1usize;
8

9
    while let Some(mut node) = head {
10
      head = node.next.take();
11
      node.next = None;
12
      data.push(node);
13
      if data.len() == sz {
14
        if sz % 2 == 0 {
15
          data.reverse();
16
        }
17
        for p in data {
18
          tail = &mut tail.insert(p).next;
19
        }
20
        data = vec![];
21
        sz += 1;
22
      }
23
    }
24

25
    if data.len() > 0 {
26
      if data.len() % 2 == 0 {
27
        data.reverse();
28
      }
29
      for p in data {
30
        tail = &mut tail.insert(p).next;
31
      }
32
    }
33

34
    ret
35
  }
36
}