LeetCode-in-All
206. Reverse Linked List
Easy
Given the head of a singly linked list, reverse the list, and return the reversed list.
Example 1:
Input: head = [1,2,3,4,5]
Output: [5,4,3,2,1]
Example 2:
Input: head = [1,2]
Output: [2,1]
Example 3:
Input: head = []
Output: []
Constraints:
- The number of nodes in the list is the range
[0, 5000]. -5000 <= Node.val <= 5000
Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?
Solution
// Definition for singly-linked list.
// 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(mut head: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
let mut prev: Option<Box<ListNode>> = None;
let mut curr = head;
while let Some(mut node) = curr {
curr = node.next.take(); // Move the next node to curr
node.next = prev; // Reverse the current node's next pointer
prev = Some(node); // Move prev forward to the current node
}
prev
}
}