added merge two sorted linked lists

Author: saihariG

LinkedList/MergeSortedLinkedLists.java

@@ -0,0 +1,149 @@
+package LinkedList;
+
+import java.util.Scanner;
+
+public class MergeSortedLinkedLists {
+
+    static class ListNode {
+        int data;
+        ListNode next;
+
+        public ListNode(int data) {
+            this.data = data;
+            this.next = null;
+        }
+    }
+
+    static class SinglyLinkedList {
+        public ListNode head;
+        public ListNode tail;
+
+        public SinglyLinkedList() {
+            this.head = null;
+            this.tail = null;
+        }
+
+        public void insertNode(int nodeData) {
+            ListNode node = new ListNode(nodeData);
+
+            if (this.head == null) {
+                this.head = node;
+            } else {
+                this.tail.next = node;
+            }
+            this.tail = node;
+        }
+    }
+
+    public static void printSinglyLinkedList(ListNode node)  {
+        while (node != null) {
+            System.out.print(node.data);
+            node = node.next;
+
+            if (node != null) {
+                System.out.print(" ");
+            }
+        }
+    }
+
+    /*
+      Given pointers to the heads of two sorted linked lists, merge them into a single sorted linked list. Either head pointer may be null meaning that the corresponding list is empty.
+     */
+    static ListNode mergeLists(ListNode head1, ListNode head2) {
+        if(head1 == null) {
+            return head2;
+        }
+
+        if(head2 == null) {
+            return head1;
+        }
+
+        ListNode current1 = head1, current2 = head2;
+        ListNode head = null, tail = null;
+
+        if(current1.data <= current2.data) {
+            head = current1;
+            tail = current1;
+            current1= current1.next;
+        }
+        else {
+            head = current2;
+            tail = current2;
+            current2 =  current2.next;
+        }
+
+        while(current1 != null && current2 != null) {
+            if(current1.data <= current2.data) {
+                tail.next = current1;
+                tail = current1;
+                current1 = current1.next;
+            } else {
+                tail.next = current2;
+                tail = current2;
+                current2 = current2.next;
+            }
+
+        }
+
+        if(current1 != null) {
+            tail.next = current1;
+        } else {
+            tail.next = current2;
+        }
+        return head;
+    }
+
+    static ListNode mergeListsRecursive(ListNode head1 , ListNode head2) {
+
+        if (head1 == null) {
+            return head2;
+        } else if (head2 == null) {
+            return head1;
+        }
+
+        if (head1.data < head2.data) {
+            head1.next = mergeListsRecursive(head1.next, head2);
+            return head1;
+        } else {
+            head2.next = mergeListsRecursive(head1, head2.next);
+            return head2;
+        }
+    }
+
+    public static void main(String[] args) {
+
+        Scanner sc = new Scanner(System.in);
+        int tests = sc.nextInt();
+
+        for (int testsItr = 0; testsItr < tests; testsItr++) {
+            SinglyLinkedList list1 = new SinglyLinkedList();
+
+            int list1Count = sc.nextInt();
+
+            for (int i = 0; i < list1Count; i++) {
+                int list1Item = sc.nextInt();
+                list1.insertNode(list1Item);
+            }
+
+            SinglyLinkedList list2 = new SinglyLinkedList();
+
+            int list2Count = sc.nextInt();
+
+
+            for (int i = 0; i < list2Count; i++) {
+                int list2Item = sc.nextInt();
+                list2.insertNode(list2Item);
+            }
+
+            ListNode list3 = mergeListsRecursive(list1.head, list2.head);
+
+
+            System.out.print("Recursive Call : ");
+            printSinglyLinkedList(list3);
+
+
+        }
+
+    }
+
+}