Reverse Linked List
Description
Given the head
of a singly linked list, reverse the list, and return the reversed list.
Example 1:
![](https://assets.leetcode.com/uploads/2021/02/19/rev1ex1.jpg)
Input: head = [1,2,3,4,5] Output: [5,4,3,2,1]
Example 2:
![](https://assets.leetcode.com/uploads/2021/02/19/rev1ex2.jpg)
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(javascript)
/**
* Definition for singly-linked list.
* function ListNode(val, next) {
* this.val = (val===undefined ? 0 : val)
* this.next = (next===undefined ? null : next)
* }
*/
/**
* @param {ListNode} head
* @return {ListNode}
*/
var reverseList = function(head) {
let prevNode = null;
let currNode = head;
while (currNode) {
let nextNode = currNode.next;
currNode.next = prevNode;
prevNode = currNode;
currNode = nextNode;
}
return prevNode;
// Time = O(n)
// Space = O(1)
};