wohhie

public static void main(String[] args) {

  Optional<String> hello = Optional.ofNullable(null);

   // 1. Optional Use:
  // check value is present in hello
   System.out.println(hello.isPresent());
  // check if hello(v) is empty
   System.out.println(hello.isEmpty());

wohhie

/*          FIND SOMEONE WITH GIVEN EMAIL ADDRESS
             * ==========================================================================*/
            studentRepository
                    .findStudentByEmail("[email protected]")
                    .ifPresentOrElse(
                            System.out::println,
                            ()-> System.out.println("Student with email [email protected] not found"));

wohhie

public int findNthLinkedList(Node head, int n) {
    Node runner = head;
    Node walker = head;

    for (int i = 0; i < n; i++){
        runner = runner.next;
    }
    if (runner == null) return head.next.data;

    while (runner != null){

wohhie

static boolean hasCycle(SinglyLinkedListNode head) {
    SinglyLinkedListNode first = head;
    SinglyLinkedListNode second = head;
    do{
        first = first.next;
        second = second.next;
        second = second != null ? second.next : null;

    }while (first != null  && second != null && first != second);

wohhie

public Node insertData(Node llist, int data){
    // Write your code here
    Node curr = llist;
    Node node = new Node(data);

    if (llist == null) return node;
    else if(node.data < curr.data){
        // insert in the beginning
        node.next = curr;
        curr.prev = node;

wohhie

public static SinglyLinkedListNode reverse(SinglyLinkedListNode llist) {
// Write your code here
    SinglyLinkedListNode curr = llist;
    SinglyLinkedListNode next = llist.next;
    
    llist.next = null;   // 1->null
    
    while(next != null){
        SinglyLinkedListNode temp = next.next;  // 3->4->5
        next.next = curr;       // 2->1->null

wohhie

public void traverse(int[][] G, int start){
    int[] visited = new int[G.length];
    Queue<Integer> queue = new LinkedList<>();

    System.out.print(start + " ");
    // visited first 1 node
    visited[start] = 1;
    // insert into the queue
    queue.add(start);

wohhie

public static int[] visited = new int[8];
public void traverse(int[][] G, int u){
    if (visited[u] == 0){
        System.out.print(u + " ");
        visited[u] = 1;

        for (int v = 1; v <G.length; v++){
            if (G[u][v] == 1 && visited[v] == 0){
                traverse(G, v);
            }

wohhie

public static int coinChange(int[] coins, int amount){
  return recursionHelper(coins, amount);
}

private static int recursionHelper(int[] coins, int remaining) {
    if (remaining == 0) return 0;
    if (remaining < 0) return -1;

    int minCount = Integer.MAX_VALUE;
    for (int coin: coins){

wohhie

public int[] plusOne(int[] digits) {
    // digits = [1, 2, 3] // output: [1, 2, 4]
    // digits = [9, 9, 9] // output: [1, 0, 0, 0]
    
    for(int idx = digits.length - 1; idx >= 0; idx--){
        if(digits[idx] < 9){
            digits[idx] += 1;
            return digits;
        }