Create 430-flatten-a-multilevel-doubly-linked-list.js

Author: everthis

430-flatten-a-multilevel-doubly-linked-list.js

@@ -0,0 +1,31 @@
+/**
+ * // Definition for a Node.
+ * function Node(val,prev,next,child) {
+ *    this.val = val;
+ *    this.prev = prev;
+ *    this.next = next;
+ *    this.child = child;
+ * };
+ */
+/**
+ * @param {Node} head
+ * @return {Node}
+ */
+const flatten = function (head) {
+  const handle = (node, next = null) => {
+    if (!node) return null;
+    handle(node.next, next);
+    const child = handle(node.child, node.next);
+    if (!node.next && next) {
+      node.next = next;
+      next.prev = node;
+    }
+    if (child) {
+      node.next = child;
+      node.child = null;
+      child.prev = node;
+    }
+    return node;
+  };
+  return handle(head);
+};