Add solution #101

Author: JoshCrozier

README.md

@@ -41,6 +41,7 @@
 83|[Remove Duplicates from Sorted List](./0083-remove-duplicates-from-sorted-list.js)|Easy|
 88|[Merge Sorted Array](./0088-merge-sorted-array.js)|Easy|
 94|[Binary Tree Inorder Traversal](./0094-binary-tree-inorder-traversal.js)|Easy|
+101|[Symmetric Tree](./0101-symmetric-tree.js)|Easy|
 102|[Binary Tree Level Order Traversal](./0102-binary-tree-level-order-traversal.js)|Medium|
 104|[Maximum Depth of Binary Tree](./0104-maximum-depth-of-binary-tree.js)|Easy|
 111|[Minimum Depth of Binary Tree](./0111-minimum-depth-of-binary-tree.js)|Easy|

solutions/0101-symmetric-tree.js

@@ -0,0 +1,34 @@
+/**
+ * 101. Symmetric Tree
+ * https://leetcode.com/problems/symmetric-tree/
+ * Difficulty: Easy
+ *
+ * Given the root of a binary tree, check whether it is a mirror
+ * of itself (i.e., symmetric around its center).
+ */
+
+/**
+ * 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 {TreeNode} root
+ * @return {boolean}
+ */
+var isSymmetric = function(root) {
+  return isBalanced(root.left, root.right);
+};
+
+function isBalanced(a, b) {
+  if (!a && !b) {
+    return true;
+  }
+  if (!a || !b) {
+    return false;
+  }
+  return a.val === b.val && isBalanced(a.left, b.right) && isBalanced(a.right, b.left);
+}