This class extends the {@link SinglyLinkedList} class to support the merging of two sorted linked lists. + * It provides a static method, `merge`, that takes two sorted singly linked lists, merges them into a single sorted linked list, + * and returns the result.
+ * + *Example usage:
+ *
+ * SinglyLinkedList listA = new SinglyLinkedList();
+ * SinglyLinkedList listB = new SinglyLinkedList();
+ * for (int i = 2; i <= 10; i += 2) {
+ * listA.insert(i); // listA: 2->4->6->8->10
+ * listB.insert(i - 1); // listB: 1->3->5->7->9
+ * }
+ * SinglyLinkedList mergedList = MergeSortedSinglyLinkedList.merge(listA, listB);
+ * System.out.println(mergedList); // Output: 1->2->3->4->5->6->7->8->9->10
+ *
+ *
+ * The `merge` method assumes that both input lists are already sorted in ascending order. + * It returns a new singly linked list that contains all elements from both lists in sorted order.
+ * + * @see SinglyLinkedList + */ public class MergeSortedSinglyLinkedList extends SinglyLinkedList { - public static void main(String[] args) { - SinglyLinkedList listA = new SinglyLinkedList(); - SinglyLinkedList listB = new SinglyLinkedList(); - - for (int i = 2; i <= 10; i += 2) { - listA.insert(i); - listB.insert(i - 1); - } - assert listA.toString().equals("2->4->6->8->10"); - assert listB.toString().equals("1->3->5->7->9"); - assert merge(listA, listB).toString().equals("1->2->3->4->5->6->7->8->9->10"); - } - /** - * Merge two sorted SingleLinkedList + * Merges two sorted singly linked lists into a single sorted singly linked list. * - * @param listA the first sorted list - * @param listB the second sored list - * @return merged sorted list + *This method does not modify the input lists; instead, it creates a new merged linked list + * containing all elements from both lists in sorted order.
+ * + * @param listA The first sorted singly linked list. + * @param listB The second sorted singly linked list. + * @return A new singly linked list containing all elements from both lists in sorted order. + * @throws NullPointerException if either input list is null. */ public static SinglyLinkedList merge(SinglyLinkedList listA, SinglyLinkedList listB) { + if (listA == null || listB == null) { + throw new NullPointerException("Input lists must not be null."); + } + Node headA = listA.getHead(); Node headB = listB.getHead(); - int size = listA.size() + listB.size(); Node head = new Node(); @@ -40,12 +58,10 @@ public class MergeSortedSinglyLinkedList extends SinglyLinkedList { } tail = tail.next; } - if (headA == null) { - tail.next = headB; - } - if (headB == null) { - tail.next = headA; - } + + // Attach remaining nodes + tail.next = (headA == null) ? headB : headA; + return new SinglyLinkedList(head.next, size); } } diff --git a/src/test/java/com/thealgorithms/datastructures/lists/MergeSortedSinglyLinkedListTest.java b/src/test/java/com/thealgorithms/datastructures/lists/MergeSortedSinglyLinkedListTest.java new file mode 100644 index 000000000..b6b785f43 --- /dev/null +++ b/src/test/java/com/thealgorithms/datastructures/lists/MergeSortedSinglyLinkedListTest.java @@ -0,0 +1,90 @@ +package com.thealgorithms.datastructures.lists; + +import static org.junit.jupiter.api.Assertions.assertEquals; +import static org.junit.jupiter.api.Assertions.assertThrows; + +import org.junit.jupiter.api.Test; + +class MergeSortedSinglyLinkedListTest { + + @Test + void testMergeTwoSortedLists() { + SinglyLinkedList listA = new SinglyLinkedList(); + SinglyLinkedList listB = new SinglyLinkedList(); + + for (int i = 2; i <= 10; i += 2) { + listA.insert(i); + listB.insert(i - 1); + } + + SinglyLinkedList mergedList = MergeSortedSinglyLinkedList.merge(listA, listB); + assertEquals("1->2->3->4->5->6->7->8->9->10", mergedList.toString(), "Merged list should contain all elements in sorted order."); + } + + @Test + void testMergeWithEmptyListA() { + SinglyLinkedList listA = new SinglyLinkedList(); // Empty listA + SinglyLinkedList listB = new SinglyLinkedList(); + listB.insert(1); + listB.insert(3); + listB.insert(5); + + SinglyLinkedList mergedList = MergeSortedSinglyLinkedList.merge(listA, listB); + assertEquals("1->3->5", mergedList.toString(), "Merged list should match listB when listA is empty."); + } + + @Test + void testMergeWithEmptyListB() { + SinglyLinkedList listA = new SinglyLinkedList(); + SinglyLinkedList listB = new SinglyLinkedList(); // Empty listB + listA.insert(2); + listA.insert(4); + listA.insert(6); + + SinglyLinkedList mergedList = MergeSortedSinglyLinkedList.merge(listA, listB); + assertEquals("2->4->6", mergedList.toString(), "Merged list should match listA when listB is empty."); + } + + @Test + void testMergeWithBothEmptyLists() { + SinglyLinkedList listA = new SinglyLinkedList(); // Empty listA + SinglyLinkedList listB = new SinglyLinkedList(); // Empty listB + + SinglyLinkedList mergedList = MergeSortedSinglyLinkedList.merge(listA, listB); + assertEquals("", mergedList.toString(), "Merged list should be empty when both input lists are empty."); + } + + @Test + void testMergeWithDuplicateValues() { + SinglyLinkedList listA = new SinglyLinkedList(); + SinglyLinkedList listB = new SinglyLinkedList(); + + listA.insert(1); + listA.insert(3); + listA.insert(5); + listB.insert(1); + listB.insert(4); + listB.insert(5); + + SinglyLinkedList mergedList = MergeSortedSinglyLinkedList.merge(listA, listB); + assertEquals("1->1->3->4->5->5", mergedList.toString(), "Merged list should include duplicate values in sorted order."); + } + + @Test + void testMergeThrowsExceptionOnNullInput() { + SinglyLinkedList listA = null; + SinglyLinkedList listB = new SinglyLinkedList(); + listB.insert(1); + listB.insert(2); + + SinglyLinkedList finalListA = listA; + SinglyLinkedList finalListB = listB; + assertThrows(NullPointerException.class, () -> MergeSortedSinglyLinkedList.merge(finalListA, finalListB), "Should throw NullPointerException if listA is null."); + + listA = new SinglyLinkedList(); + listB = null; + SinglyLinkedList finalListA1 = listA; + SinglyLinkedList finalListB1 = listB; + assertThrows(NullPointerException.class, () -> MergeSortedSinglyLinkedList.merge(finalListA1, finalListB1), "Should throw NullPointerException if listB is null."); + } +}