7.1_LinkedList_pop.js

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

class LinkedList {
	constructor(value) {
		const newNode = new Node(value)
		this.head = newNode
		this.tail = this.head
		this.length = 1
	}

	printList() {
		let temp = this.head
		while (temp !== null) {
			console.log(temp.value)
			temp = temp.next
		}
	}

	getHead() {
		if (this.head === null) {
			console.log('Head: null')
		} else {
			console.log('Head: ' + this.head.value)
		}
	}

	getTail() {
		if (this.tail === null) {
			console.log('Tail: null')
		} else {
			console.log('Tail: ' + this.tail.value)
		}
	}

	getLength() {
		console.log('Length: ' + this.length)
	}

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

	push(value) {
		const newNode = new Node(value)
		if (!this.head) {
			this.head = newNode
			this.tail = newNode
		} else {
			this.tail.next = newNode
			this.tail = newNode
		}
		this.length++
		return this
	}

	/// WRITE POP METHOD HERE ///
	pop() {
		if (!this.head) return undefined
		let temp = this.head
		let pre = this.head
		while (temp.next) {
			pre = temp
			temp = temp.next
		}
		this.tail = pre
		this.tail.next = null
		this.length--
		if (this.length === 0) {
			this.head = null
			this.tail = null
		}
		return temp
	}
}

function test() {
	let myLinkedList = new LinkedList(1)
	myLinkedList.push(2)

	// (2) Items in LL - Returns 2 Node
	if (myLinkedList.length !== 0) {
		console.log(myLinkedList.pop().value)
	} else {
		console.log('null')
	}

	// (1) Item in LL - Returns 1 Node
	if (myLinkedList.length !== 0) {
		console.log(myLinkedList.pop().value)
	} else {
		console.log('null')
	}

	// (0) Items in LL - Returns null
	if (myLinkedList.length !== 0) {
		console.log(myLinkedList.pop().value)
	} else {
		console.log('null')
	}
}

test()

/*
    EXPECTED OUTPUT:
    ----------------
    2
    1
    null

*/