Committing code related Nth Node from Last Node

Author: Arunkumarvarada

DataStructures/LinkedList/com/java4u/ds/linkedlist/nthNode/NthNodeFromLast.java

@@ -3,29 +3,28 @@
 import com.java4u.ds.linkedlist.Node;
 
 public class NthNodeFromLast {
-	public Node NthNodeFromEnd(Node head, int n) {
-		Node temp = head;
-		Node pthNode = null;
-		for (int i = 0; i < n; i++) {
-			if (temp != null) {
-				temp = temp.getNext();
-			}
+	public int NthNodeFromEnd(Node head, int nodeFromLast) {
+
+		if (nodeFromLast <= 0 || head == null) {
+			return -1;
 		}
-		while (temp != null) {
-			if (pthNode != null) {
-				pthNode = head;
-			} else {
-				pthNode = pthNode.getNext();
+
+		Node ptrA = head, ptrB = head;
+
+		for (int i = 0; i < nodeFromLast; i++) {
+
+			if (ptrB == null) {
+				return -1;
 			}
-			temp = temp.getNext();
+			ptrB = ptrB.getNext();
 		}
-
-		if (pthNode != null) {
-			return pthNode;
-		} else {
-			return null;
+		while (ptrB != null) {
+			ptrB = ptrB.getNext();
+			ptrA = ptrA.getNext();
 		}
 
+		return ptrA.getData();
+
 	}
 
 	public static void main(String[] args) {
@@ -42,10 +41,7 @@ public static void main(String[] args) {
 		n2.setNext(n3);
 		n3.setNext(n4);
 		n4.setNext(n5);
-		Node node = list.NthNodeFromEnd(head, 2);
-		if (node != null) {
-			System.out.println(node.getData());
-		}
+		System.out.println(list.NthNodeFromEnd(head, 2));
 
 	}
 }

DataStructures/LinkedList/com/java4u/ds/linkedlist/nthNode/NthNodeFromLastUsingRecursion.java

@@ -7,33 +7,15 @@ public class NthNodeFromLastUsingRecursion {
 	int count = 0;
 
 	public int nthNodeFromEnd(Node head, int nodeFromLast) {
-
-		if (nodeFromLast <= 0 || head == null) {
+		if (head == null) {
 			return -1;
 		}
-
-		Node ptrA = head, ptrB = head;
-
-		// Moving ptrB N nodes from start keeping ptrA at head node.
-		for (int i = 0; i < nodeFromLast; i++) {
-
-			// If ptrB reaches NULL, then return -1 as indication that given Nth value is
-			// incorrect and list doesn't contain N elements.
-			if (ptrB == null) {
-				return -1;
-			}
-			ptrB = ptrB.getNext();
-		}
-
-		// Now incrementing ptrA and ptrB one node at a time until ptrB encounters NULL,
-		// when it encounters NULL then ptrA will be at Nth position from end of list.
-		while (ptrB != null) {
-			ptrB = ptrB.getNext();
-			ptrA = ptrA.getNext();
+		int data = nthNodeFromEnd(head.getNext(), nodeFromLast);
+		count++;
+		if (count == nodeFromLast) {
+			return head.getData();
 		}
-
-		return ptrA.getData();
-
+		return data;
 	}
 
 	public static void main(String[] args) {