单链表反转两种方法

https://www.cnblogs.com/mwl523/p/10749144.html

package com.example.myapplication


import android.os.Bundle
import android.util.Log
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {
    var message = ""
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        var A = Node("A")
        var B = Node("B")
        var C = Node("C")
        var D = Node("D")

        A.next = B
        B.next = C
        C.next = D
        D.next = null
        printNode(A)
        Log.e("ssssss", message)

        message = ""
        var newNode = reverseNode(A)
        printNode(newNode)
        Log.e("ssssss", message)

    }

    private fun reverseNode(a: Node?): Node? {
        var preNode: Node? = null
        var nextNode: Node? = null
        var curNode: Node? = a
        while (curNode != null) {
            nextNode = curNode.next
            curNode.next = preNode
            preNode = curNode
            curNode = nextNode
        }
        return preNode
    }


    private fun printNode(a: Node?) {
        if (a == null) {
            return
        }
        if (a.next != null) {
            message += (a.name + "->")
            printNode(a.next)
        } else {
            message += (a.name + "-> NULL")
        }
    }
}

import java.util.*


fun main() {
    val listNode = ListNode(1)
    val listNode2 = ListNode(2)
    val listNode3 = ListNode(3)
    val listNode4 = ListNode(4)
    listNode.next = listNode2
    listNode2.next = listNode3
    listNode3.next = listNode4
    listNode4.next = null
    val result = reverseListNode(listNode)
    print(result.toString())
}


private fun reverseListNode(listNode: ListNode): ListNode {
    var temp: ListNode? = listNode
    var result = ListNode(-1)
    while (temp != null) {
        var pNext = temp.next
        temp.next = result.next
        result.next = temp
        temp = pNext
    }
    return result.next!!
}

 class ListNode(var value: Int) {
    var next: ListNode? = null
    var hasNext: Boolean = (next != null)
    override fun toString(): String {
        val stack: Stack<Int> = Stack()
        var temp: ListNode? = this
        while (temp != null) {
            stack.push(temp.value)
            temp = temp.next
        }
        val arraylist: ArrayList<Int> = ArrayList()
        while (!stack.isEmpty()){
            arraylist.add(stack.pop())
        }
        arraylist.reverse()
        return arraylist.toString()
    }
}