Create Solution.java

Author: Jerring

solution/0430.Flatten a Multilevel Doubly Linked List/Solution.java

@@ -0,0 +1,32 @@
+class Solution {
+    public Node flatten(Node head) {
+        if (head == null) {
+            return null;
+        }
+        dfs(head);
+        head.prev = null;
+        return head;
+    }
+
+    private Node dfs(Node head) {
+        Node cur = head;
+        while (cur != null) {
+            head.prev = cur;
+            Node next = cur.next;
+            if (cur.child != null) {
+                Node h = dfs(cur.child);
+                cur.child = null;
+                Node t = h.prev;
+                cur.next = h;
+                h.prev = cur;
+                t.next = next;
+                if (next != null) {
+                    next.prev = t;
+                }
+                head.prev = t;
+            }
+            cur = next;
+        }
+        return head;
+    }
+}