Add solution #536

Author: JoshCrozier

README.md

@@ -521,6 +521,7 @@
 532|[K-diff Pairs in an Array](./solutions/0532-k-diff-pairs-in-an-array.js)|Medium|
 533|[Lonely Pixel II](./solutions/0533-lonely-pixel-ii.js)|Medium|
 535|[Encode and Decode TinyURL](./solutions/0535-encode-and-decode-tinyurl.js)|Medium|
+536|[Construct Binary Tree from String](./solutions/0536-construct-binary-tree-from-string.js)|Medium|
 537|[Complex Number Multiplication](./solutions/0537-complex-number-multiplication.js)|Medium|
 538|[Convert BST to Greater Tree](./solutions/0538-convert-bst-to-greater-tree.js)|Medium|
 539|[Minimum Time Difference](./solutions/0539-minimum-time-difference.js)|Medium|

solutions/0536-construct-binary-tree-from-string.js

@@ -0,0 +1,64 @@
+/**
+ * 536. Construct Binary Tree from String
+ * https://leetcode.com/problems/construct-binary-tree-from-string/
+ * Difficulty: Medium
+ *
+ * You need to construct a binary tree from a string consisting of parenthesis and integers.
+ *
+ * The whole input represents a binary tree. It contains an integer followed by zero, one or
+ * two pairs of parenthesis. The integer represents the root's value and a pair of parenthesis
+ * contains a child binary tree with the same structure.
+ *
+ * You always start to construct the left child node of the parent first if it exists.
+ */
+
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {string} s
+ * @return {TreeNode}
+ */
+var str2tree = function(s) {
+  if (!s) return null;
+  let index = 0;
+  return constructTree();
+
+  function parseNumber() {
+    const isNegative = s[index] === '-';
+    if (isNegative) index++;
+
+    let num = 0;
+    while (index < s.length && /[0-9]/.test(s[index])) {
+      num = num * 10 + parseInt(s[index]);
+      index++;
+    }
+
+    return isNegative ? -num : num;
+  }
+
+  function constructTree() {
+    if (index >= s.length) return null;
+
+    const value = parseNumber();
+    const node = new TreeNode(value);
+    if (index < s.length && s[index] === '(') {
+      index++;
+      node.left = constructTree();
+      index++;
+    }
+
+    if (index < s.length && s[index] === '(') {
+      index++;
+      node.right = constructTree();
+      index++;
+    }
+
+    return node;
+  }
+};