LINKED_LIST.js

class Node {
  constructor(x,next){
    this.value = x;
    this.next = next;
  }

}

class LinkedList {

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

addToHead(x){
  // empty and not empty
const   newNode = new Node(x,null);
// no  node 
if(this.head === null && this.tail === null ){
       this.head = newNode;
       this.tail = newNode;
}
//one node 
 else{
   newNode.next = this.head;
   this.head = newNode;
 }
}
addToTail(x){
  const newNode = new Node(x, null);
  // no  node 
  if( this.head === null  && this.tail === null){
       this.tail = newNode;
       this.head = newNode; 
       return;
  } 
  // one node or more  
  else {
        this.tail.next = newNode;
         this.tail = newNode;
      }   
  }

removeFromHead(){
 if(!this.head){
    return 
 }
 // move the head to the next node 
   this.head = this.head.next
}

removeFromtail(){

 let current = this.head.next;
 let previous = this.head;

 if(!this.tail){
    return 
 }
else  if(current === null){
  this.tail = null;
  this.head = null;
 }
 else{
   // we move along the chain 
   while(current.next !== null){
       previous = current;
       current = current.next;
   }
   // we release the last node 
   this.tail =  previous;
   this.tail.next = null;
 }
}


getSize(){
let count = 0;
let current = this.head;
if(current === null ) console.log(" count ==> 0 ");
// loop through all nods from head to tail
while(current !== null){
     ++count;
     current = current.next;
}
console.log('size ===> ', count);
return count;
}



// remove at index
removeAtIndex(index){
  if(this.tail === this.head && this.tail === null){
    console.log("empty");
    return; 
  }
   if(this.head === this.tail && index === 0 ){
      this.head = null;
      this.tail = null;
      return;
   }

    if(index === 0){
     this.head = this.head.next
      return;
   }

let  previous = this.head;
let  current = this.head.next;


const size = this.getSize();

/* 
we start the count from 1 because
 previous is the one is counting for us , and 
 it has one  aready one (this.head)
  */
let  count = 1;

/** 
  n1 - n2 - n3 -n4 -n5 .... 
  remeber that prevoius is at n1.
  we are making the condition count < index
  because the index start from 0, and the count start from 1. 
  So let say we want the 4th node to be pulled out, then the  index is 
  3, and the count is 4. 
  the condition for the loop to stop at the count 2, means prvious will 
  be moving only 2 nodes ahead , so previous will be at n3, and current at n4
  we make previous leapfrog n4 to connect to n5 (current.next)
 */
while(count <  index){
  previous = current;
  count++;
  current = current.next; 
}
previous.next = current.next;
}


// printing 
printValues(){
  let current = null;
  if(this.head === null  ){
      return null;
  }
current = this.head;
while(current !== null ){
   console.log(current.value);
   current = current.next;
  }
  return;
}

// remove random value x;
removeValue(x){ 
  // empty list 
  if( this.head === null) return "it is empty"; 
  // there is only one node and it value = x 
  if(this.head === this.tail  && this.head.value === x){
        this.head = null;
        this.tail = null;
        return;
  }

 // the first node has value of x ; ===> "@"
  if(this.head.value === x ){
   this.head = this.head.next;
}

let previous = this.head ;
let current = this.head.next;


//keep moving looking for x in the rest of the nodes
 while(current !== null){
   // we want to check the current, because previous is check in ===> "@"
  if(current.value === x) {
    current = current.next;
    previous.next = current;
    continue;
  }
     previous = current;
     current = current.next
    
};
// the list is finished 
   return; 
 }

}// end of LinkedList

const ll = new LinkedList();
 ll.addToHead(7);
 ll.addToHead(8);
 ll.addToHead(9);
 ll.addToTail(1)
 ll.addToTail(2)
ll.addToTail(3)
ll.addToTail(4)
ll.addToHead(3)

// ll.removeFromHead()
// ll.removeFromHead()
// ll.removeFromtail()

//  ll.removeValue(4);
  ll.removeValue(3);
  ll.removeValue(7);


  ll.removeAtIndex(4);
   //ll.removeAtIndex(3);
  // ll.removeValue(7)


ll.getSize();  
ll.printValues()