feat: add javascript solution to lc problem: No.0110.Balanced Binary Tree (#405)

Author: zhaocchen

solution/0100-0199/0110.Balanced Binary Tree/README.md

@@ -116,6 +116,34 @@ class Solution {
 }
 ```
 
+### **JavaScript**
+
+```js
+/**
+ * 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 isBalanced = function(root) {
+    if (root == null) return true; 
+    let left = root.left;
+    let right = root.right;
+    return isBalanced(left) && isBalanced(right) && Math.abs(depth(left) - depth(right)) <= 1;
+};
+
+function depth(root) {
+    if (root == null) return 0;
+    return Math.max(depth(root.left), depth(root.right)) + 1;
+}
+```
+
 ### **C++**
 
 ```cpp

solution/0100-0199/0110.Balanced Binary Tree/README_EN.md

@@ -106,6 +106,34 @@ class Solution {
 }
 ```
 
+### **JavaScript**
+
+```js
+/**
+ * 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 isBalanced = function(root) {
+    if (root == null) return true; 
+    let left = root.left;
+    let right = root.right;
+    return isBalanced(left) && isBalanced(right) && Math.abs(depth(left) - depth(right)) <= 1;
+};
+
+function depth(root) {
+    if (root == null) return 0;
+    return Math.max(depth(root.left), depth(root.right)) + 1;
+}
+```
+
 ### **C++**
 
 ```cpp

solution/0100-0199/0110.Balanced Binary Tree/Solution.js

@@ -0,0 +1,23 @@
+/**
+ * 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 isBalanced = function(root) {
+    if (root == null) return true; 
+    let left = root.left;
+    let right = root.right;
+    return isBalanced(left) && isBalanced(right) && Math.abs(depth(left) - depth(right)) <= 1;
+};
+
+function depth(root) {
+    if (root == null) return 0;
+    return Math.max(depth(root.left), depth(root.right)) + 1;
+}