feat: created unshift linkedlist method

src/DataStructures/LinkedList.js

@@ -1,3 +1,5 @@
+import { isValidNumber } from "../Maths";
+
 export class Node {
 	constructor(value) {
 		this.value = value;
@@ -7,10 +9,16 @@ export class Node {
 
 export class LinkedList {
 	constructor(value) {
-		const newNode = new Node(value);
-		this.head = newNode;
-		this.tail = newNode;
-		this.size = 1;
+		if (isValidNumber(value)) {
+			const newNode = new Node(value);
+			this.head = newNode;
+			this.tail = newNode;
+			this.size = 1;
+		} else {
+			this.head = null;
+			this.tail = null;
+			this.size = 0;
+		}
 	}
 
 	print() {
@@ -46,7 +54,7 @@ export class LinkedList {
 
 	// Remove a value from the END of the list
 	pop() {
-		if (this.size === 0) return undefined;
+		if (!this.size) return undefined;
 
 		let pre = this.head;
 		let temp = this.head;
@@ -56,7 +64,7 @@ export class LinkedList {
 		}
 
 		this.tail = pre;
-		pre.next = null;
+		this.tail.next = null;
 
 		this.size--;
 
@@ -66,6 +74,14 @@ export class LinkedList {
 
 	// Add a new value to the BEGINNING of the list
 	unshift(value) {
+		const newNode = new Node(value);
+		newNode.next = this.head;
+		this.head = newNode;
+
+		if (!this.tail) this.tail = newNode;
+
+		this.size++;
+
 		return this;
 	}
 

tests/DataStructures/LinkedList.test.js

@@ -18,6 +18,13 @@ describe("LinkedList.js", () => {
 
 				expect(ll.size).toBe(1);
 			});
+
+			it("creates a new empty LinkedList", () => {
+				const ll = new LinkedList();
+				expect(ll.size).toBe(0);
+				expect(ll.head).toBe(null);
+				expect(ll.tail).toBe(null);
+			});
 		});
 
 		describe("clear()", () => {
@@ -95,6 +102,45 @@ describe("LinkedList.js", () => {
 			});
 		});
 
+		describe("unshift()", () => {
+			it("should add a new element at the start", () => {
+				const ll = new LinkedList(0);
+
+				ll.unshift(10);
+				expect(ll.size).toBe(2);
+				expect(ll.head.value).toBe(10);
+				expect(ll.tail.value).toBe(0);
+				expect(ll.tail.next).toBe(null);
+				expect(ll.toArray()).toEqual([10, 0]);
+
+				ll.unshift(20);
+				expect(ll.size).toBe(3);
+				expect(ll.head.value).toBe(20);
+				expect(ll.tail.value).toBe(0);
+				expect(ll.tail.next).toBe(null);
+				expect(ll.toArray()).toEqual([20, 10, 0]);
+			});
+
+			it("should add a new element if the list is empty", () => {
+				const ll = new LinkedList();
+				expect(ll.size).toBe(0);
+
+				ll.unshift(1);
+				expect(ll.size).toBe(1);
+				expect(ll.head.value).toBe(1);
+				expect(ll.tail.value).toBe(1);
+				expect(ll.tail.next).toBe(null);
+				expect(ll.toArray()).toEqual([1]);
+
+				ll.unshift(10);
+				expect(ll.size).toBe(2);
+				expect(ll.head.value).toBe(10);
+				expect(ll.tail.value).toBe(1);
+				expect(ll.tail.next).toBe(null);
+				expect(ll.toArray()).toEqual([10, 1]);
+			});
+		});
+
 		describe("toArray()", () => {
 			it("should return an array with the values of the linked list", () => {
 				const ll = new LinkedList(0);
@@ -104,8 +150,6 @@ describe("LinkedList.js", () => {
 
 				const result = ll.toArray();
 
-				console.log(result);
-
 				expect(Array.isArray(result)).toBe(true);
 				expect(result).toEqual([0, 10, 20, 30]);
 			});