反转链表

题目： https://leetcode-cn.com/problems/reverse-linked-list/

多指针

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func reverseList(head *ListNode) *ListNode {

    var prev *ListNode
    for head != nil  {
        // next := head.Next
        // head.Next = prev
        // prev = head
        // head = next
        head.Next, prev, head =  prev, head, head.Next
    }
    return prev
}

递归YYDS

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func reverseList(head *ListNode) *ListNode {


    if head == nil || head.Next == nil {
        return head
    }
    curr := reverseList(head.Next)
    head.Next.Next = head
    head.Next = nil
    return curr
}