added solution for 430

Author: ashmichheda

src/main/java/com/fishercoder/common/classes/DoublyLinkedNode.java

@@ -0,0 +1,15 @@
+package com.fishercoder.common.classes;
+
+public class DoublyLinkedNode {
+    public int val;
+    public DoublyLinkedNode next;
+    public DoublyLinkedNode prev;
+    public DoublyLinkedNode child;
+    public DoublyLinkedNode(int i) {
+        this.val = i;
+    }
+
+    public int val() {
+        return val;
+    }
+}

src/main/java/com/fishercoder/solutions/_430.java

@@ -0,0 +1,40 @@
+package com.fishercoder.solutions;
+
+import com.fishercoder.common.classes.DoublyLinkedNode;
+
+/**
+ * Idea is to implement a recursive strategy by calling the recursiveFlatten() method, recursively on the child node of the parent Node
+ *
+ */
+public class _430 {
+    public static class Solution{
+        private DoublyLinkedNode recursiveFlatten(DoublyLinkedNode head){
+            DoublyLinkedNode current = head, tail = head;
+            while(current != null){
+                DoublyLinkedNode child = current.child;
+                DoublyLinkedNode next = current.next;
+                if(child != null){
+                    DoublyLinkedNode output = recursiveFlatten(child);
+                    output.next = next;
+                    if(next != null)
+                        next.prev = output;
+                    current.next = child;
+                    child.prev = current;
+                    current.child = null;
+                }
+                else{
+                    current = next;
+                }
+                if(current != null){
+                    tail = current;
+                }
+            }
+            return tail;
+        }
+        public DoublyLinkedNode flatten(DoublyLinkedNode head) {
+            if(head != null)
+                recursiveFlatten(head);
+            return head;
+        }
+    }
+}