Adding first method to retrieve first n items in the list ordered head to tail

Author: sfkiwi

src/index.ts

@@ -209,22 +209,21 @@ export class LinkedList<T> {
     return currentItem.value;
   }
 
-  toArray(): T[] {
-    return [...this];
-    // let arr: T[] = [];
-    // let currentItem = this._head;
+  first(num: number): T[] {
+    let iter = this.iterator();
+    let result = [];
 
-    // while (true) {
-    //   arr.push(currentItem.value);
+    let n = Math.min(num, this.length);
 
-    //   if (currentItem.next) {
-    //     currentItem = currentItem.next;
-    //   } else {
-    //     break;
-    //   }
-    // }
+    for (let i = 0; i < n; i++) {
+      let val = iter.next();
+      result.push(val.value);
+    }
+    return result;
+  }
 
-    // return arr;
+  toArray(): T[] {
+    return [...this];
   }
 
   private isDuplicate(val: T): boolean {

test/LinkedListTest.ts

@@ -484,4 +484,43 @@ describe('Linked-List Tests', () => {
     let result = list.toArray()
     expect(result.length).to.equal(0);
   });
+
+  it('should return the first n values of the list', () => {
+    let values: number[] = [4, 5, 6, 7, 8, 9]
+    let list = new LinkedList<number>(...values);
+    expect(list.length).to.equal(6);
+    expect(list.head).to.equal(4);
+    expect(list.tail).to.equal(9);
+    let result = list.first(3);
+    expect(result.length).to.equal(3);
+    expect(result[0]).to.equal(4);
+    expect(result[1]).to.equal(5);
+    expect(result[2]).to.equal(6);
+  });
+
+  it('should return empty array when n is zero', () => {
+    let values: number[] = [4, 5, 6, 7, 8, 9]
+    let list = new LinkedList<number>(...values);
+    expect(list.length).to.equal(6);
+    expect(list.head).to.equal(4);
+    expect(list.tail).to.equal(9);
+    let result = list.first(0);
+    expect(result.length).to.equal(0);
+  });
+
+  it('should return the lesser of n values or length of list', () => {
+    let values: number[] = [4, 5, 6, 7, 8, 9]
+    let list = new LinkedList<number>(...values);
+    expect(list.length).to.equal(6);
+    expect(list.head).to.equal(4);
+    expect(list.tail).to.equal(9);
+    let result = list.first(7);
+    expect(result.length).to.equal(6);
+    expect(result[0]).to.equal(4);
+    expect(result[1]).to.equal(5);
+    expect(result[2]).to.equal(6);
+    expect(result[3]).to.equal(7);
+    expect(result[4]).to.equal(8);
+    expect(result[5]).to.equal(9);
+  })
 });