Reverse Linked List (pointer Iterative)

I/O:

addFirst 10 addFirst 20 addLast 30 addLast 40 addLast 50 addFirst 60 removeAt 2 display reversePI display quit

O/P:

60 20 30 40 50 50 40 30 20 60

temp = cur.next

Now we can do,

cur.next = prev

prev = cur

cur = temp

So, after this operation it will look like this:

We will again store the next pointer in temp.

temp = curr.next

Now we can do the reversing part,

cur.next = prev

prev = cur

cur = temp

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Reverse_A_Linked_List_pointerIterative {
    public static class Node {
        int data;
        Node next;
    }

    public static class LinkedList {
        Node head;
        Node tail;
        int size;

        void addLast(int val) {
            Node temp = new Node();
            temp.data = val;
            temp.next = null;

            if (size == 0) {
                head = tail = temp;
            } else {
                tail.next = temp;
                tail = temp;
            }

            size++;
        }

        public int size() {
            return size;
        }

        public void display() {
            for (Node temp = head; temp != null; temp = temp.next) {
                System.out.print(temp.data + " ");
            }
            System.out.println();
        }

        public void removeFirst() {
            if (size == 0) {
                System.out.println("List is empty");
            } else if (size == 1) {
                head = tail = null;
                size = 0;
            } else {
                head = head.next;
                size--;
            }
        }

        public int getFirst() {
            if (size == 0) {
                System.out.println("List is empty");
                return -1;
            } else {
                return head.data;
            }
        }

        public int getLast() {
            if (size == 0) {
                System.out.println("List is empty");
                return -1;
            } else {
                return tail.data;
            }
        }

        public int getAt(int idx) {
            if (size == 0) {
                System.out.println("List is empty");
                return -1;
            } else if (idx < 0 || idx >= size) {
                System.out.println("Invalid arguments");
                return -1;
            } else {
                Node temp = head;
                for (int i = 0; i < idx; i++) {
                    temp = temp.next;
                }
                return temp.data;
            }
        }

        public void addFirst(int val) {
            Node temp = new Node();
            temp.data = val;
            temp.next = head;
            head = temp;

            if (size == 0) {
                tail = temp;
            }

            size++;
        }

        public void addAt(int idx, int val) {
            if (idx < 0 || idx > size) {
                System.out.println("Invalid arguments");
            } else if (idx == 0) {
                addFirst(val);
            } else if (idx == size) {
                addLast(val);
            } else {
                Node node = new Node();
                node.data = val;

                Node temp = head;
                for (int i = 0; i < idx - 1; i++) {
                    temp = temp.next;
                }
                node.next = temp.next;

                temp.next = node;
                size++;
            }
        }

        public void removeLast() {
            if (size == 0) {
                System.out.println("List is empty");
            } else if (size == 1) {
                head = tail = null;
                size = 0;
            } else {
                Node temp = head;
                for (int i = 0; i < size - 2; i++) {
                    temp = temp.next;
                }

                tail = temp;
                tail.next = null;
                size--;
            }
        }

        public void removeAt(int idx) {
            if (idx < 0 || idx >= size) {
                System.out.println("Invalid arguments");
            } else if (idx == 0) {
                removeFirst();
            } else if (idx == size - 1) {
                removeLast();
            } else {
                Node temp = head;
                for (int i = 0; i < idx - 1; i++) {
                    temp = temp.next;
                }

                temp.next = temp.next.next;
                size--;
            }
        }

        private Node getNodeAt(int idx) {
            Node temp = head;
            for (int i = 0; i < idx; i++) {
                temp = temp.next;
            }
            return temp;
        }

        public void reverseDI() {
            int li = 0;
            int ri = size - 1;
            while (li < ri) {
                Node left = getNodeAt(li);
                Node right = getNodeAt(ri);

                int temp = left.data;
                left.data = right.data;
                right.data = temp;

                li++;
                ri--;
            }
        }

        // write your code here
        public void reversePI() {
            Node previous = null;
            Node current = head;
            Node forward = head.next;

            while (current != null) {
                forward = current.next;         // save the existing
                current.next = previous;        // shift the pointer to previous
                previous = current;             // shift previous to current
                current = forward;              // shift current to forward

            }
            tail = head;
            head = previous;
        }
    }

    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        LinkedList list = new LinkedList();

        String str = br.readLine();
        while (str.equals("quit") == false) {
            if (str.startsWith("addLast")) {
                int val = Integer.parseInt(str.split(" ")[1]);
                list.addLast(val);
            } else if (str.startsWith("size")) {
                System.out.println(list.size());
            } else if (str.startsWith("display")) {
                list.display();
            } else if (str.startsWith("removeFirst")) {
                list.removeFirst();
            } else if (str.startsWith("getFirst")) {
                int val = list.getFirst();
                if (val != -1) {
                    System.out.println(val);
                }
            } else if (str.startsWith("getLast")) {
                int val = list.getLast();
                if (val != -1) {
                    System.out.println(val);
                }
            } else if (str.startsWith("getAt")) {
                int idx = Integer.parseInt(str.split(" ")[1]);
                int val = list.getAt(idx);
                if (val != -1) {
                    System.out.println(val);
                }
            } else if (str.startsWith("addFirst")) {
                int val = Integer.parseInt(str.split(" ")[1]);
                list.addFirst(val);
            } else if (str.startsWith("addAt")) {
                int idx = Integer.parseInt(str.split(" ")[1]);
                int val = Integer.parseInt(str.split(" ")[2]);
                list.addAt(idx, val);
            } else if (str.startsWith("removeLast")) {
                list.removeLast();
            } else if (str.startsWith("removeAt")) {
                int idx = Integer.parseInt(str.split(" ")[1]);
                list.removeAt(idx);
            } else if (str.startsWith("reverseDI")) {
                list.reverseDI();
            } else if (str.startsWith("reversePI")) {
                list.reversePI();
            }
            str = br.readLine();
        }
    }
}