feat: add MergeTwoSortedLinkedLIsts algorithms (#1442)

* feat: add mergeTwoSortedLinkedLIsts algorithms

* remove class and unnecessary function

change the function params and return value from Node to LinkedList.

Author: ahnge

Diff for: Data-Structures/Linked-List/MergeTwoSortedLinkedLists.js

@@ -0,0 +1,45 @@
+import { LinkedList } from './SinglyLinkedList.js'
+/**
+ * A LinkedList-based solution for merging two sorted linked lists into one sorted list.
+ *
+ * @param {LinkedList} list1 - The the first sorted linked list.
+ * @param {LinkedList} list2 - The second sorted linked list.
+ * @returns {LinkedList} - The merged sorted linked list.
+ *
+ * @example
+ * const list1 = new LinkedList([1,2,4]);
+ *
+ * const list2 = new LinkedList([1,3,4]);
+ *
+ * const result = mergeLinkedLists(list1, list2);
+ * // Returns the merged linked list representing 1 -> 1 -> 2 -> 3 -> 4 -> 4
+ */
+
+function mergeLinkedLists(list1, list2) {
+  const mergedList = new LinkedList()
+
+  let current1 = list1.headNode
+  let current2 = list2.headNode
+
+  while (current1 || current2) {
+    if (!current1) {
+      mergedList.addLast(current2.data)
+      current2 = current2.next
+    } else if (!current2) {
+      mergedList.addLast(current1.data)
+      current1 = current1.next
+    } else {
+      if (current1.data < current2.data) {
+        mergedList.addLast(current1.data)
+        current1 = current1.next
+      } else {
+        mergedList.addLast(current2.data)
+        current2 = current2.next
+      }
+    }
+  }
+
+  return mergedList
+}
+
+export { mergeLinkedLists }

Diff for: Data-Structures/Linked-List/test/MergeTwoSortedLinkedLists.test.js

@@ -0,0 +1,39 @@
+import { expect } from 'vitest'
+import { mergeLinkedLists } from '../MergeTwoSortedLinkedLists.js'
+import { LinkedList } from '../SinglyLinkedList.js'
+
+describe('MergeTwoSortedLinkedLists', () => {
+  it('Merges two sorted linked lists', () => {
+    const list1 = new LinkedList([1, 2, 4])
+
+    const list2 = new LinkedList([1, 3, 4])
+
+    const expectedResult = new LinkedList([1, 1, 2, 3, 4, 4])
+
+    const result = mergeLinkedLists(list1, list2)
+
+    expect(result).toEqual(expectedResult)
+  })
+
+  it('Merges two empty linked lists', () => {
+    const list1 = new LinkedList()
+    const list2 = new LinkedList()
+
+    const expectedResult = new LinkedList()
+
+    const result = mergeLinkedLists(list1, list2)
+
+    expect(result).toEqual(expectedResult)
+  })
+
+  it('Merges one empty linked list with a non-empty one', () => {
+    const list1 = new LinkedList()
+    const list2 = new LinkedList([1])
+
+    const expectedResult = new LinkedList([1])
+
+    const result = mergeLinkedLists(list1, list2)
+
+    expect(result).toEqual(expectedResult)
+  })
+})