RecursiveReversePrint_LinkedList.java

import java.io.*;
import java.util.*;

public class Main {
  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--;
      }
    }

    public void reversePI() {
      if (size <= 1) {
        return;
      }

      Node prev = null;
      Node curr = head;
      while (curr != null) {
        Node next = curr.next;

        curr.next = prev;
        prev = curr;
        curr = next;
      }

      Node temp = head;
      head = tail;
      tail = temp;
    }

    public int kthFromLast(int k) {
      Node slow = head;
      Node fast = head;
      for (int i = 0; i < k; i++) {
        fast = fast.next;
      }

      while (fast != tail) {
        slow = slow.next;
        fast = fast.next;
      }

      return slow.data;
    }

    public int mid() {
      Node f = head;
      Node s = head;

      while (f.next != null && f.next.next != null) {
        f = f.next.next;
        s = s.next;
      }

      return s.data;
    }

    public static LinkedList mergeTwoSortedLists(LinkedList l1, LinkedList l2) {
      LinkedList ml = new LinkedList();

      Node one = l1.head;
      Node two = l2.head;
      while (one != null && two != null) {
        if (one.data < two.data) {
          ml.addLast(one.data);
          one = one.next;
        } else {
          ml.addLast(two.data);
          two = two.next;
        }
      }

      while (one != null) {
        ml.addLast(one.data);
        one = one.next;
      }

      while (two != null) {
        ml.addLast(two.data);
        two = two.next;
      }

      return ml;
    }

    public static Node midNode(Node head, Node tail) {
      Node f = head;
      Node s = head;

      while (f != tail && f.next != tail) {
        f = f.next.next;
        s = s.next;
      }

      return s;
    }

    public static LinkedList mergeSort(Node head, Node tail) {
      if (head == tail) {
        LinkedList br = new LinkedList();
        br.addLast(head.data);
        return br;
      }

      Node mid = midNode(head, tail);
      LinkedList fsh = mergeSort(head, mid);
      LinkedList ssh = mergeSort(mid.next, tail);
      LinkedList sl = mergeTwoSortedLists(fsh, ssh);
      return sl;
    }

    public void removeDuplicates() {
      LinkedList res = new LinkedList();

      while (this.size() > 0) {
        int val = this.getFirst();
        this.removeFirst();

        if (res.size() == 0 || val != res.tail.data) {
          res.addLast(val);
        }
      }

      this.head = res.head;
      this.tail = res.tail;
      this.size = res.size;
    }

    public void oddEven() {
      LinkedList odd = new LinkedList();
      LinkedList even = new LinkedList();

      while (this.size > 0) {
        int val = this.getFirst();
        this.removeFirst();

        if (val % 2 == 0) {
          even.addLast(val);
        } else {
          odd.addLast(val);
        }
      }

      if (odd.size > 0 && even.size > 0) {
        odd.tail.next = even.head;

        this.head = odd.head;
        this.tail = even.tail;
        this.size = odd.size + even.size;
      } else if (odd.size > 0) {
        this.head = odd.head;
        this.tail = odd.tail;
        this.size = odd.size;
      } else if (even.size > 0) {
        this.head = even.head;
        this.tail = even.tail;
        this.size = even.size;
      }
    }

    public void kReverse(int k) {
      LinkedList prev = null;

      while (this.size > 0) {
        LinkedList curr = new LinkedList();

        if (this.size >= k) {
          for (int i = 0; i < k; i++) {
            int val = this.getFirst();
            this.removeFirst();
            curr.addFirst(val);
          }
        } else {
          int sz = this.size;
          for (int i = 0; i < sz; i++) {
            int val = this.getFirst();
            this.removeFirst();
            curr.addLast(val);
          }
        }

        if (prev == null) {
          prev = curr;
        } else {
          prev.tail.next = curr.head;
          prev.tail = curr.tail;
          prev.size += curr.size;
        }
      }

      this.head = prev.head;
      this.tail = prev.tail;
      this.size = prev.size;
    }

    private void displayReverseHelper(Node node){
      if(node == null)
      {
          return ;
      }
      displayReverseHelper(node.next);
      System.out.print(node.data + " ");
    }

    public void displayReverse(){
      displayReverseHelper(head);
      System.out.println();
    }
  }

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

    int n1 = Integer.parseInt(br.readLine());
    LinkedList l1 = new LinkedList();
    String[] values1 = br.readLine().split(" ");
    for (int i = 0; i < n1; i++) {
      int d = Integer.parseInt(values1[i]);
      l1.addLast(d);
    }
    
    int a = Integer.parseInt(br.readLine());
    int b = Integer.parseInt(br.readLine());

    l1.display();
    l1.displayReverse();
    l1.addLast(a);
    l1.addFirst(b);
    l1.display();
  }
}