pub fn is_palindrome(mut head: Option<Box<ListNode>>) -> bool {

if head.is_none() { return true; }

let mut N = 0;

let mut href = head.as_ref();

while let Some(node) = href {

href = node.next.as_ref();

N += 1;

}

let mut hmut = head.as_mut();

let mut mid = N / 2 - 1;

while mid > 0 {

hmut = hmut.unwrap().next.as_mut();

mid -= 1;

}

let mut prev = None;

let mut next = hmut.unwrap().next.take();

while let Some(mut next_inner) = next {

next = next_inner.next.take();

next_inner.next = prev.take();

prev = Some(next_inner);

}

let mut h1 = &head;

let mut h2 = &prev;

loop {

let (not_equal, should_break) = match (h1.as_ref(), h2.as_ref()) {

(Some(h1_inner), Some(h2_inner)) => {

h1 = &h1_inner.next;

h2 = &h2_inner.next;

(h1_inner.val != h2_inner.val, false)

},

_ => (false, true)

};

if should_break { break; }

if not_equal { return false; }

}

return true;

}