Update 19.java

Author: SaimantikaBasu

leetcode/java/linkedlist/19.java

@@ -10,37 +10,28 @@
  */
 class Solution {
     public ListNode removeNthFromEnd(ListNode head, int n) {
-        ListNode dummy = new ListNode(0);
-        dummy.next = head;
-        ListNode first = dummy;
-        ListNode second = dummy;
+        if(n==0 || head==null)
+            return head;
+        if(n==1 && head.next==null)
+            return null;
 
-        for (int i = 0; i < n; i++) { 
-  
-            // If count of nodes in the given 
-            // linked list is <= N 
-            if (second.next == null) { 
-  
-                // If count = N i.e. delete the head node 
-                if (i == n - 1) 
-                    first = first.next; 
-                
-            } 
-            second = second.next; 
-        } 
-  
-        // Increment both the pointers by one until 
-        // second pointer reaches the end 
-        while (second.next != null) { 
-            first = first.next; 
-            second = second.next; 
-        } 
-  
-        // First must be pointing to the 
-        // Nth node from the end by now 
-        // So, delete the node first is pointing to 
-        first.next = first.next.next; 
-        return dummy.next;
+        ListNode fast=head;
+        ListNode slow=head;
+        while(n-->0)
+            fast=fast.next;
+        if(fast==null)
+            return slow.next;
+        while(fast.next!=null)
+        {
+            fast=fast.next;
+            slow=slow.next;
+        }
+        
+        ListNode fwd=slow.next;
+        slow.next=fwd.next;
+        fwd.next=null;
+        
+        return head;
     } 
 
-}
+}