type SinglyNode<T> = {
  value: T;
  next: SinglyNode<T> | null;
};

// ตัวอย่างการสร้าง singly linked list ด้วย object literal
const node3 = { value: 30, next: null };
const node2 = { value: 20, next: node3 };
const node1 = { value: 10, next: node2 };
const head = node1;

// Traverse: 10 → 20 → 30 → null

function printList(head) {
  let current = head;

  while (current !== null) {
    console.log(current.value);
    current = current.next;
  }
}

const head = { value: 10, next: { value: 20, next: { value: 30, next: null } } };
printList(head);
// 10
// 20
// 30

function getAt(head, index) {
  let current = head;
  let count = 0;

  while (current !== null) {
    if (count === index) return current.value;
    count += 1;
    current = current.next;
  }

  return undefined; // index เกินขนาด list
}

const head = { value: 10, next: { value: 20, next: { value: 30, next: null } } };
console.log(getAt(head, 0)); // 10
console.log(getAt(head, 2)); // 30
console.log(getAt(head, 5)); // undefined

function find(head, target) {
  let current = head;
  let index = 0;

  while (current !== null) {
    if (current.value === target) return index;
    current = current.next;
    index += 1;
  }

  return -1; // ไม่พบ
}

const head = { value: 10, next: { value: 20, next: { value: 30, next: null } } };
console.log(find(head, 20));  // 1
console.log(find(head, 99));  // -1

class SinglyList {
  constructor() {
    this.head = null;
    this.tail = null;
  }

  prepend(value) {
    const node = { value, next: this.head };
    this.head = node;
    if (!this.tail) this.tail = node;
  }

  print() {
    let current = this.head;
    const values = [];

    while (current !== null) {
      values.push(current.value);
      current = current.next;
    }

    console.log(values.join(" → "));
  }

  find(target) {
    let current = this.head;
    let index = 0;

    while (current !== null) {
      if (current.value === target) return index;
      current = current.next;
      index += 1;
    }

    return -1;
  }
}

const list = new SinglyList();
list.prepend(30);
list.prepend(20);
list.prepend(10);
list.print(); // 10 → 20 → 30
console.log(list.find(20)); // 1