Update JavaScript code for Balanced Binary Tree

The JavaScript solution for 110 - Balanced Binary Tree currently
available on the NeetCode.io website is inefficient, with a time
complexity of O(n^2). I have updated the solution to reflect the
original Python solution as presented in the video.

Author: YashSingh15

javascript/110-Balanced-Binary-Tree.js

@@ -10,17 +10,19 @@
  * @param {TreeNode} root
  * @return {boolean}
  */
- var isBalanced = function (root) {
-    if (!root) return true
-    const left = findHeight(root.left)
-    const right = findHeight(root.right)
-    return Math.abs(left - right) <= 1 && isBalanced(root.left) && isBalanced(root.right)
-};
+var isBalanced = function (root) {
+    const getHeight = (root) => {
+        if (!root) return [-1, true];
 
-function findHeight(node) {
-    if (node == null) return 0;
-    return 1 + Math.max(this.findHeight(node.left), this.findHeight(node.right));
-}
+        const [leftHeight, leftBalanced] = getHeight(root.left);
+        const [rightHeight, rightBalanced] = getHeight(root.right);
 
-// Runtime: 78 ms, faster than 90.43% of JavaScript online submissions for Balanced Binary Tree.
-// Memory Usage: 47.1 MB, less than 32.41% of JavaScript online submissions for Balanced Binary Tree.
+        const balanced = leftBalanced && rightBalanced && Math.abs(leftHeight - rightHeight) < 2;
+
+        return [1 + Math.max(leftHeight, rightHeight), balanced];
+    };
+
+    const balanced = getHeight(root)[1]
+    
+    return balanced;
+};