Reverse Linked List

linked.js

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var reverseList = function(head) {
    if (!head) {
        return head;
    }
    var currentNode = head.next;
    
    if (!currentNode) {
        return head;
    }
    
    var previousNode = head;
    var nextNode = currentNode.next;
    var last;
    while(currentNode) {
        currentNode.next = previousNode;
        
        previousNode = currentNode;
        currentNode = nextNode;
        if (currentNode) {
            nextNode = currentNode.next;
        } else {
            last = previousNode;
        }
    }
    head.next = null;
    
    return last;
};