Add solution #606

Author: JoshCrozier

solutions/0606-construct-string-from-binary-tree.js

@@ -0,0 +1,41 @@
+/**
+ * 606. Construct String from Binary Tree
+ * https://leetcode.com/problems/construct-string-from-binary-tree/
+ * Difficulty: Easy
+ *
+ * You need to construct a string consists of parenthesis and integers
+ * from a binary tree with the preorder traversing way.
+ *
+ * The null node needs to be represented by empty parenthesis pair "()".
+ * And you need to omit all the empty parenthesis pairs that don't
+ * affect the one-to-one mapping relationship between the string
+ * and the original binary tree.
+ */
+
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+/**
+ * @param {TreeNode} t
+ * @return {string}
+ */
+var tree2str = function(t) {
+  return !t ? '' : `${t.val}(${tree2str(t.left)})(${tree2str(t.right)})`.replace(/(\(\)){2}|\(\)(?=$|\))/g, '');
+};
+
+
+// alternative, longer but faster version:
+/**
+ * @param {TreeNode} t
+ * @return {string}
+ */
+var tree2str = function(t) {
+  let str = t ? `${t.val}` : '';
+  if (t && t.right) str += `(${tree2str(t.left)})(${tree2str(t.right)})`;
+  else if (t && t.left) str += `(${tree2str(t.left)})`;
+  return str;
+};