feat: add mergeTwoSortedLinkedLIsts algorithms

Author: ahnge

Data-Structures/Linked-List/MergeTwoSortedLinkedLists.js

@@ -0,0 +1,64 @@
+import { Node } from './SinglyLinkedList.js'
+/**
+ * A LinkedList-based solution for merging two sorted linked lists into one sorted list.
+ *
+ * @param {Node} list1 - The head of the first sorted linked list.
+ * @param {Node} list2 - The head of the second sorted linked list.
+ * @returns {Node} - The head of the merged sorted linked list.
+ *
+ * @example
+ * const list1 = new ListNode(1);
+ * list1.next = new ListNode(2);
+ * list1.next.next = new ListNode(4);
+ *
+ * const list2 = new ListNode(1);
+ * list2.next = new ListNode(3);
+ * list2.next.next = new ListNode(4);
+ *
+ * const result = mergeLists(list1, list2);
+ * // Returns the head of a linked list representing 1 -> 1 -> 2 -> 3 -> 4 -> 4
+ */
+
+class MergeTwoSortedLinkedLists {
+  mergeLists(list1, list2) {
+    let dummy = new Node(-1)
+    let current = dummy
+
+    while (list1 && list2) {
+      if (list1.val < list2.val) {
+        current.next = list1
+        list1 = list1.next
+      } else {
+        current.next = list2
+        list2 = list2.next
+      }
+      current = current.next
+    }
+
+    // If one of the lists is not empty, append it to the result
+    if (list1) {
+      current.next = list1
+    } else if (list2) {
+      current.next = list2
+    }
+
+    return dummy.next
+  }
+
+  /**
+   * Converts a linked list to an array.
+   *
+   * @param {Node} head - The head of the linked list.
+   * @returns {number[]} - An array representing the linked list values.
+   */
+  linkedListToArray(head) {
+    const resultArray = []
+    while (head) {
+      resultArray.push(head.val)
+      head = head.next
+    }
+    return resultArray
+  }
+}
+
+export { MergeTwoSortedLinkedLists }

Data-Structures/Linked-List/test/MergeTwoSortedLinkedLists.test.js

@@ -0,0 +1,54 @@
+import { MergeTwoSortedLinkedLists } from '../MergeTwoSortedLinkedLists.js'
+import { Node } from '../SinglyLinkedList.js'
+
+describe('MergeTwoSortedLinkedLists', () => {
+  it('Merges two sorted linked lists', () => {
+    const list1 = new Node(1)
+    list1.next = new Node(2)
+    list1.next.next = new Node(4)
+
+    const list2 = new Node(1)
+    list2.next = new Node(3)
+    list2.next.next = new Node(4)
+
+    const expectedResult = new Node(1)
+    expectedResult.next = new Node(1)
+    expectedResult.next.next = new Node(2)
+    expectedResult.next.next.next = new Node(3)
+    expectedResult.next.next.next.next = new Node(4)
+    expectedResult.next.next.next.next.next = new Node(4)
+
+    const merger = new MergeTwoSortedLinkedLists()
+    const result = merger.mergeLists(list1, list2)
+
+    expect(merger.linkedListToArray(result)).toEqual(
+      merger.linkedListToArray(expectedResult)
+    )
+  })
+
+  it('Merges two empty linked lists', () => {
+    const list1 = null
+    const list2 = null
+
+    const expectedResult = null
+
+    const merger = new MergeTwoSortedLinkedLists()
+    const result = merger.mergeLists(list1, list2)
+
+    expect(result).toEqual(expectedResult)
+  })
+
+  it('Merges one empty linked list with a non-empty one', () => {
+    const list1 = null
+    const list2 = new Node(0)
+
+    const expectedResult = new Node(0)
+
+    const merger = new MergeTwoSortedLinkedLists()
+    const result = merger.mergeLists(list1, list2)
+
+    expect(merger.linkedListToArray(result)).toEqual(
+      merger.linkedListToArray(expectedResult)
+    )
+  })
+})