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Linked List Reversal

  • Understanding linked list reversal
  • Solved problems are presented in alphabetical order
Reverse Linked List

↗ See LeetCode Problem #206​

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode() {} *     ListNode(int val) { this.val = val; } *     ListNode(int val, ListNode next) { this.val = val; this.next = next; } * } */class ListNode {    int data;    ListNode next;    ListNode(int data) {        this.data = data;        this.next = null;    }}//class LinkedList {////////}class Solution {//    static ListNode reverseList(ListNode head) {    static int reverseList(ListNode head) {        ListNode prev = null;        while (head != null) {            ListNode next = head.next;            head.next = prev;            prev = head;            head = next;        }//        return prev;        return prev.data;    }    static int countNodes (ListNode head) {        int count = 1;        ListNode current = head;        while (current.next != null){            current = current.next;            count++;        }        return count;    }    public static void main(String[] args) {        int[] headArray = {1,2,3,4,5};        ListNode head = new ListNode(headArray[0]);        ListNode current = head;        for (int i = 1; i < headArray.length; i++) {            ListNode node = new ListNode(headArray[i]);            current.next = node;            current = node;        }//        ListNode nodeA = new ListNode(1);//        ListNode nodeB = new ListNode(2);//        ListNode nodeC = new ListNode(3);//        ListNode nodeD = new ListNode(4);//        ListNode nodeE = new ListNode(5);////        nodeA.next = nodeB;//        nodeB.next = nodeC;//        nodeC.next = nodeD;//        nodeD.next = nodeE;        System.out.println(countNodes(head));        System.out.println(reverseList(head));//        System.out.println();//        System.out.println(countNodes(nodeA));//        System.out.println(reverseList(nodeA));    }}