generics.ts

// Implement generic for two way linked list for different items type.

interface ILinkedList<T> {
  append(value: T);
  pop():T|null;
  showlist():void;
}

class LinkedList<T> implements ILinkedList<T> {
  public head:MyNode<T>
  public tail:MyNode<T>
  public length:number

  constructor(){
    this.head = null
    this.tail = null
    this.length = 0
  }

  public append(value: T):MyNode<T> {
    let node = new MyNode<T>(value)
    this.head = this.head || node

    if (this.tail) {
      this.tail.next = node
      node.prev = this.tail
    }

    this.tail = node
    this.length += 1

    return node
  }

  // Is it correct?
  public pop(): T|null {
    if (!this.head) { return null }

    let _tail = this._pop()

    if (!this.tail) {
      this.head = null
    }

    this.length -= 1
    return _tail.value
  }

  public showlist():void {
    console.log('Length:', this.length)

    let _node = this.head
    while (_node) {
      console.log('Node Value:', _node.value)
      _node = _node.next
    }
  }

  private _pop():MyNode<T> {
    let _node = this.tail
    this.tail = this.tail.prev

    if (this.tail) {
      this.tail.next = null
    }

    return _node
  }
}

class MyNode<T> {
  public value = null
  public next = null
  public prev = null

  constructor(val: T){
    this.value = val
  }
}


const ll = new LinkedList
ll.append(10)
ll.append('20')
ll.append(30)
ll.pop()
ll.append('150')
ll.append(200)
ll.pop()
ll.append({ hello: 'world' })
ll.append(function(){ let idle })
ll.append(NaN)
ll.append(undefined)
ll.append(40)

ll.showlist()