feat: solve new question

Author: arwildo

balanced-binary-tree/main.js

@@ -0,0 +1,35 @@
+/**
+ * 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)
+ * }
+
+root = [3,9,20,null,null,15,7]
+
+            3
+           / \
+          9   20
+             /  \
+            15   7
+
+ */
+/**
+ * @param {TreeNode} root
+ * @return {boolean}
+ */
+var isBalanced = function(root) {
+    
+    function dfs(root) {
+        if (root == null) return [true, 0];
+
+        let left = dfs(root.left);
+        let right = dfs(root.right);
+
+        let balanced = (left[0] && right[0] && Math.abs(left[1] - right[1]) <= 1);
+        return [balanced, 1 + Math.max(left[1], right[1])];
+    }
+
+    return dfs(root)[0];
+};