* Update SinglyLinkedList

* Refactor MergeSortedSinglyLinkedList to single file
* Create Problem09 and Problem10 in Project Euler

DataStructures/Lists/MergeSortedSinglyLinkedList.java

@@ -0,0 +1,51 @@
+package DataStructures.Lists;
+
+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
+     *
+     * @param listA the first sorted list
+     * @param listB the second sored list
+     * @return merged sorted list
+     */
+    public static SinglyLinkedList merge(SinglyLinkedList listA, SinglyLinkedList listB) {
+        Node headA = listA.getHead();
+        Node headB = listB.getHead();
+
+        int size = listA.size() + listB.size();
+
+        Node head = new Node();
+        Node tail = head;
+        while (headA != null && headB != null) {
+            if (headA.value <= headB.value) {
+                tail.next = headA;
+                headA = headA.next;
+            } else {
+                tail.next = headB;
+                headB = headB.next;
+            }
+            tail = tail.next;
+        }
+        if (headA == null) {
+            tail.next = headB;
+        }
+        if (headB == null) {
+            tail.next = headA;
+        }
+        return new SinglyLinkedList(head.next, size);
+    }
+}