Add solution #431

Author: JoshCrozier

README.md

@@ -419,6 +419,7 @@
 428|[Serialize and Deserialize N-ary Tree](./solutions/0428-serialize-and-deserialize-n-ary-tree.js)|Hard|
 429|[N-ary Tree Level Order Traversal](./solutions/0429-n-ary-tree-level-order-traversal.js)|Medium|
 430|[Flatten a Multilevel Doubly Linked List](./solutions/0430-flatten-a-multilevel-doubly-linked-list.js)|Medium|
+431|[Encode N-ary Tree to Binary Tree](./solutions/0431-encode-n-ary-tree-to-binary-tree.js)|Hard|
 432|[All O`one Data Structure](./solutions/0432-all-oone-data-structure.js)|Hard|
 433|[Minimum Genetic Mutation](./solutions/0433-minimum-genetic-mutation.js)|Medium|
 434|[Number of Segments in a String](./solutions/0434-number-of-segments-in-a-string.js)|Easy|

solutions/0431-encode-n-ary-tree-to-binary-tree.js

@@ -0,0 +1,74 @@
+/**
+ * 431. Encode N-ary Tree to Binary Tree
+ * https://leetcode.com/problems/encode-n-ary-tree-to-binary-tree/
+ * Difficulty: Hard
+ *
+ * Design an algorithm to encode an N-ary tree into a binary tree and decode the binary tree
+ * to get the original N-ary tree. An N-ary tree is a rooted tree in which each node has no
+ * more than N children. Similarly, a binary tree is a rooted tree in which each node has no
+ * more than 2 children. There is no restriction on how your encode/decode algorithm should
+ * work. You just need to ensure that an N-ary tree can be encoded to a binary tree and this
+ * binary tree can be decoded to the original N-nary tree structure.
+ *
+ * Nary-Tree input serialization is represented in their level order traversal, each group
+ * of children is separated by the null value (See following example).
+ *
+ * For example, you may encode the following 3-ary tree to a binary tree in this way:
+ * - Input: root = [1,null,3,2,4,null,5,6]
+ *
+ * Note that the above is just an example which might or might not work. You do not necessarily
+ * need to follow this format, so please be creative and come up with different approaches yourself.
+ */
+
+/**
+ * // Definition for a _Node.
+ * function _Node(val,children) {
+ *    this.val = val;
+ *    this.children = children;
+ * };
+ */
+
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+
+class Codec {
+  constructor() {}
+
+  encode = function(root) {
+    if (!root) return null;
+
+    const binaryRoot = new TreeNode(root.val);
+
+    if (root.children.length > 0) {
+      binaryRoot.left = this.encode(root.children[0]);
+    }
+
+    let sibling = binaryRoot.left;
+    for (let i = 1; i < root.children.length; i++) {
+      if (sibling) {
+        sibling.right = this.encode(root.children[i]);
+        sibling = sibling.right;
+      }
+    }
+
+    return binaryRoot;
+  };
+
+  decode = function(root) {
+    if (!root) return null;
+
+    const updated = new _Node(root.val, []);
+    let sibling = root.left;
+    while (sibling) {
+      updated.children.push(this.decode(sibling));
+      sibling = sibling.right;
+    }
+
+    return updated;
+  };
+}