go 刷算法第一题——反转链表

一步一个脚印，弄懂吸收了，才是自己的知识

题目

输入：{1,2,3}
返回值：{3,2,1}

package main

type ListNode struct {
    Val  int
    Next *ListNode
}

func ReverseList(pHead *ListNode) *ListNode {
    // write code here
}

写法一：简单反转

func ReverseList(pHead *ListNode) *ListNode {
    // write code here
    if pHead == nil || pHead.Next == nil {
        return pHead
    }
    var newHead *ListNode
    for pHead != nil {
        // 保存下一节点值
        pNext := pHead.Next

        // 反转节点赋值
        // 当前元节点下一节点设值为反转节点
        pHead.Next = newHead
        // 反转节点等于当前元节点
        newHead = pHead

        // 下一节点作为下一次判断元节点
        pHead = pNext
    }
    return newHead
}

写法二：反转+Go平行赋值

func ReverseList( pHead *ListNode ) *ListNode {
    if pHead == nil || pHead.Next == nil{
        return pHead
    }
    var newHead *ListNode
    for pHead != nil {
        pHead, pHead.Next, newHead = pHead.Next, newHead, pHead
    }
    return newHead
}

写法三：递归

func ReverseList(head *ListNode) *ListNode {
    // write code here
    if head == nil || head.Next == nil {
        return head
    }

    res := ReverseList(head.Next)

    head.Next.Next = head
    head.Next = nil

    return res
}