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.
* class ListNode {
* int val;
* ListNode? next;
* ListNode([this.val = 0, this.next]);
* }
*/
class Solution {
ListNode? reverseList(ListNode? head) {
ListNode? curr = head;
ListNode? prev = null;
while (curr != null) {
ListNode? Next = curr.next;
curr.next = prev;
prev = curr;
curr = Next;
}
return prev;
}
}