Function reverse_list

pub fn reverse_list(head: Option<Box<ListNode>>) -> Option<Box<ListNode>>

Solutions

Approach 1: Iterative

• Time complexity: O(n)

• Space complexity: O(1)

// Definition for singly-linked list.
// #[derive(PartialEq, Eq, Debug)]
// pub struct ListNode {
//   pub val: i32,
//   pub next: Option<Box<ListNode>>
// }
//
// impl ListNode {
//   #[inline]
//   fn new(val: i32) -> Self {
//     ListNode {
//       next: None,
//       val
//     }
//   }
// }

impl Solution {
    pub fn reverse_list(head: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
	    if head.is_none() { return None; }

	    let mut prev = None;
	    let mut current = head;
	    while let Some(mut tmp) = current.take() {
	        let next = tmp.next.take();
	        tmp.next = prev.take();
	        prev = Some(tmp);
	        current = next;
	    }

	    prev
    }
}