2023-02-14 update: added "110. Balanced Binary Tree"

Author: fartem

README.md

@@ -34,3 +34,4 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 101. Symmetric Tree                             | [Link](https://leetcode.com/problems/symmetric-tree/)                             | [Link](./lib/easy/symmetric_tree.dart)                             |
 | 104. Maximum Depth of Binary Tree               | [Link](https://leetcode.com/problems/maximum-depth-of-binary-tree/description/)   | [Link](./lib/easy/maximum_depth_of_binary_tree.dart)               |
 | 108. Convert Sorted Array to Binary Search Tree | [Link](https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/) | [Link](./lib/easy/convert_sorted_array_to_binary_search_tree.dart) |
+| 110. Balanced Binary Tree                       | [Link](https://leetcode.com/problems/balanced-binary-tree/)                       | [Link](./lib/easy/balanced_binary_tree.dart)                       |

lib/easy/balanced_binary_tree.dart

@@ -0,0 +1,28 @@
+import 'dart:math';
+
+import '../common/tree_node.dart';
+
+// https://leetcode.com/problems/balanced-binary-tree/
+class Solution {
+  bool isBalanced(TreeNode? root) {
+    if (root != null) {
+      var l = _maxHeight(root.left);
+      var r = _maxHeight(root.right);
+      return (l - r).abs() < 2 &&
+          isBalanced(root.left) &&
+          isBalanced(root.right);
+    }
+    return true;
+  }
+
+  int _maxHeight(TreeNode? node) {
+    if (node != null) {
+      return 1 +
+          max(
+            _maxHeight(node.left),
+            _maxHeight(node.right),
+          );
+    }
+    return 0;
+  }
+}

test/easy/balanced_binary_tree_test.dart

@@ -0,0 +1,50 @@
+import 'package:leetcode_dart/common/tree_node.dart';
+import 'package:leetcode_dart/easy/balanced_binary_tree.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group(
+    'Example tests',
+    () {
+      final bbt = Solution();
+      test(
+        'true',
+        () => expect(
+          true,
+          bbt.isBalanced(
+            TreeNode(
+              3,
+              TreeNode(9),
+              TreeNode(
+                20,
+                TreeNode(15),
+                TreeNode(7),
+              ),
+            ),
+          ),
+        ),
+      );
+      test(
+        'false',
+        () => expect(
+          false,
+          bbt.isBalanced(
+            TreeNode(
+              1,
+              TreeNode(
+                2,
+                TreeNode(
+                  3,
+                  TreeNode(4),
+                  TreeNode(4),
+                ),
+                TreeNode(3),
+              ),
+              TreeNode(2),
+            ),
+          ),
+        ),
+      );
+    },
+  );
+}