feat: add concat()

README.md

@@ -351,6 +351,23 @@ let result = list.toArray()
 result // => [4, 5, 6, 7]
 ```
 
+#### LinkedList<T>.concat(): LinkedList<T>
+
+Allows you to concatenate two linked lists using either their heads or tails respectively.
+
+```typescript
+const listA = new LinkedList(1, 2);
+const listB = new LinkedList(-1, -2);
+const headAToHeadB = LinkedList.concat(listA, listB, 'head', 'head').toArray();
+// => [ 2, 1, -1, -2 ]
+const headAToTailB = LinkedList.concat(listA, listB, 'head', 'tail').toArray();
+// => [ -1, -2, 1, 2 ]
+const tailAToHeadB = LinkedList.concat(listA, listB, 'tail', 'head').toArray();
+// => [ 1, 2, -1, -2 ]
+const tailAToTailB = LinkedList.concat(listA, listB, 'tail', 'tail').toArray();
+// => [ 1, 2, -2, -1 ]
+```
+
 ## Attribution
 
 This linked-list was originally shared by Christos Monogios via his [blog][blog]. The [original code][origcode] has been modified and extended to support typedef generics to allow for type checking on stored values for linked lists and iterable and iterator protocols.

src/index.ts

@@ -41,6 +41,45 @@ export class LinkedList<T> {
     return this._length;
   }
 
+  /**
+   * Given two lists, it concatenates them as configured and returns a single linked list.
+   *
+   * @param listA linked list a
+   * @param listB linked list b
+   * @param listAEnd use head or tail of listA for the joint
+   * @param listBEnd use head or tail of listB for the joint
+   *
+   * @example ```ts
+   * const listA = new LinkedList(1, 2);
+   * const listB = new LinkedList(-1, -2);
+   * const headAToHeadB = LinkedList.concat(listA, listB, 'head', 'head').toArray();
+   * // => [ 2, 1, -1, -2 ]
+   * const headAToTailB = LinkedList.concat(listA, listB, 'head', 'tail').toArray();
+   * // => [ -1, -2, 1, 2 ]
+   * const tailAToHeadB = LinkedList.concat(listA, listB, 'tail', 'head').toArray();
+   * // => [ 1, 2, -1, -2 ]
+   * const tailAToTailB = LinkedList.concat(listA, listB, 'tail', 'tail').toArray();
+   * // => [ 1, 2, -2, -1 ]
+   * ```
+   */
+  static concat<T>(listA: LinkedList<T>, listB: LinkedList<T>, listAEnd: 'head' | 'tail', listBEnd: 'head' | 'tail'): LinkedList<T> {
+    const entriesA = listA.toArray();
+    const entriesB = listB.toArray();
+    if (listAEnd === 'head') {
+      if (listBEnd === 'head') {
+        entriesA.reverse();
+        return new LinkedList(...[...entriesA, ...entriesB]);
+      } else {
+        return new LinkedList(...[...entriesB, ...entriesA]);
+      }
+    } else {
+      if (listBEnd === 'tail') {
+        entriesB.reverse();
+      }
+      return new LinkedList(...[...entriesA, ...entriesB]);
+    }
+  }
+
   // Adds the element at a specific position inside the linked list
   insert(val: T, previousItem: T, checkDuplicates: boolean = false): boolean {
 

test/LinkedListTest.ts

@@ -13,6 +13,33 @@ class Foo {
 }
 
 describe('Linked-List Tests', () => {
+
+  it('should concat lists', () => {
+    const listA = new LinkedList(1, 2);
+    const listB = new LinkedList(-1, -2);
+    const headAToHeadB = LinkedList.concat(listA, listB, 'head', 'head').toArray();
+    expect(headAToHeadB[0]).to.equal(2);
+    expect(headAToHeadB[1]).to.equal(1);
+    expect(headAToHeadB[2]).to.equal(-1);
+    expect(headAToHeadB[3]).to.equal(-2);
+    const headAToTailB = LinkedList.concat(listA, listB, 'head', 'tail').toArray();
+    expect(headAToTailB[0]).to.equal(-1);
+    expect(headAToTailB[1]).to.equal(-2);
+    expect(headAToTailB[2]).to.equal(1);
+    expect(headAToTailB[3]).to.equal(2);
+    const tailAToHeadB = LinkedList.concat(listA, listB, 'tail', 'head').toArray();
+    expect(tailAToHeadB[0]).to.equal(1);
+    expect(tailAToHeadB[1]).to.equal(2);
+    expect(tailAToHeadB[2]).to.equal(-1);
+    expect(tailAToHeadB[3]).to.equal(-2);
+    const tailAToTailB = LinkedList.concat(listA, listB, 'tail', 'tail').toArray();
+    expect(tailAToTailB[0]).to.equal(1);
+    expect(tailAToTailB[1]).to.equal(2);
+    expect(tailAToTailB[2]).to.equal(-2);
+    expect(tailAToTailB[3]).to.equal(-1);
+  })
+
+
   it('should create an empty list #1', () => {
     let values: number[] = [];