算法题-反转链表【JS实现】

输入: 1->2->3->4->5->NULL
输出: 5->4->3->2->1->NULL

迭代法：

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var reverseList = function(head) {
    
    
    let [prev, curr] = [null, head]
    while(curr) {
    
    
        [curr.next, prev, curr] = [prev, curr, curr.next]
    }
    return prev
};

递归法：

var reverseList = function(head) {
    
    
    if(!head || !head.next) return head;
    let next = head.next;
    let reverseHead = reverseList(next)
    head.next = null;
    next.next = head;
    return reverseHead;
};

var reverseList = function(head) {
    
    
    function reverse (prev, curr) {
    
    
        if (!curr) return prev
        let tmp = curr.next;
        curr.next = prev;
        return reverse(curr, tmp);
    }

    return reverse(null, head)
};