Swap Nodes in Pairs.rs

// Runtime: 0 ms (Top 100.0%) | Memory: 2.10 MB (Top 85.07%)

macro_rules! next_node_as_ref {
    ($a: expr) => {
        $a.as_ref().unwrap().next
    };
}
macro_rules! next_node_as_mut {
    ($a: expr) => {
        $a.as_mut().unwrap().next
    };
}
impl Solution {
    pub fn swap_pairs(mut head: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
        if head.is_none() {
            return None;
        }
        let mut cur_node = &mut head;

        // while we have something to work with (.next has something)
        while cur_node.is_some() && next_node_as_ref!(cur_node).is_some() {
            // .take() Takes the value out of the option, leaving a None in its place.
            let mut even_node = next_node_as_mut!(cur_node).take();

            // taking next odd node's value
            let next_odd_node = next_node_as_mut!(even_node).take();
            // cur_node's .next points to next odd node
            next_node_as_mut!(cur_node) = next_odd_node;
            // even node's .next points to cur_node
            next_node_as_mut!(even_node) = cur_node.take();
            // switching cur_node with even node
            cur_node.replace(even_node.unwrap());
            // point cursor to .next.next
            cur_node = &mut next_node_as_mut!(next_node_as_mut!(cur_node));
        }
        head
    }
}