LinkedList.js

class Node{
  constructor(data) {
    this.data = data;
    this.next = null;
  }
}

class LL {
  constructor() {
    this.head = null;
  }
  
  insert(data) {
    if (!data) {
      return null;
    }
    
    let node = new Node(data);
    let current = this.head;
    
    if (current === null) {
      this.head = node;
    } else {
      while(current.next) {
        current = current.next;
      }
      current.next = node;
    }
  }
  
  remove(data) {
    if (this.head && this.head.data === data) {
      this.head = this.head.next;
    } else {
      let current = this.head;
      let prev = null;
      while(current) {
        if (current.data === data) {
          prev.next = current.next;
          break;
        }
        prev = current;
        current = current.next;
      }
    }
  }
  
  find(data) {
    let current = this.head;
    while(current) {
      if (current.data === data) {
        return current;
      }
      current = current.next;
    }
    return null;
  }
  
  print() {
    let current = this.head;
    while(current) {
      console.log(current.data);
      current = current.next;
    }
  }
  
  reverse() {
    let current = this.head;
    let prev = null;
    let next = null;
    while(current) {
      next = current.next;
      current.next = prev;
      prev = current;
      current = next;
    }
    this.head = prev;
  }
  
  nToLast(k) {
    let current = this.head;
    
    for (let i=0; i < k-1; i++) {
      current = current.next;
    }
    
    let p1 = this.head;
    
    while(current.next) {
      p1 = p1.next;
      current = current.next;
    }
    return p1;
  }
  
  hasLoop() {
    let p1 = this.head;
    let p2 = this.head;
    
    while(p2 && p2.next && p2.next.next) {
      p1 = p1.next;
      p2 = p2.next.next;
      
      if (p1 === p2) {
        return true;
      }
    }
    return false;
  }
 
}


let myList = new LL();
    
myList.insert('a');
myList.insert('b');
myList.insert('c');
myList.insert('d');
myList.insert('e');
myList.insert('f');

myList.remove('b'); 
console.log(myList.find('e')); // e --> f
console.log(JSON.stringify(myList)); // a --> c --> d --> e --> f --> null
myList.reverse();  // reverse the list f --> e --> d --> c --> a --> null
console.log(JSON.stringify(myList));

console.log(myList.nToLast(2)); // c --> a -- > next

console.log(myList.hasLoop());  // false