Binary search tree updates

config.json

@@ -348,6 +348,24 @@
         "loops",
         "math"
       ]
+    },
+    {
+      "slug": "binary-search-tree",
+      "uuid": "597f86bc-6717-4a4c-a2c6-58241ac3d6cb",
+      "core": true,
+      "unlocked_by": null,
+      "difficulty": 5,
+      "topics": [
+        "algorithms",
+        "classes",
+        "generics",
+        "inheritance",
+        "logic",
+        "object_oriented_programming",
+        "searching",
+        "sorting",
+        "trees"
+      ]
     }
   ]
 }

exercises/binary-search-tree/README.md

@@ -0,0 +1,62 @@
+# Binary Search Tree
+
+Insert and search for numbers in a binary tree.
+
+When we need to represent sorted data, an array does not make a good
+data structure.
+
+Say we have the array `[1, 3, 4, 5]`, and we add 2 to it so it becomes
+`[1, 3, 4, 5, 2]` now we must sort the entire array again! We can
+improve on this by realizing that we only need to make space for the new
+item `[1, nil, 3, 4, 5]`, and then adding the item in the space we
+added. But this still requires us to shift many elements down by one.
+
+Binary Search Trees, however, can operate on sorted data much more
+efficiently.
+
+A binary search tree consists of a series of connected nodes. Each node
+contains a piece of data (e.g. the number 3), a variable named `left`,
+and a variable named `right`. The `left` and `right` variables point at
+`nil`, or other nodes. Since these other nodes in turn have other nodes
+beneath them, we say that the left and right variables are pointing at
+subtrees. All data in the left subtree is less than or equal to the
+current node's data, and all data in the right subtree is greater than
+the current node's data.
+
+For example, if we had a node containing the data 4, and we added the
+data 2, our tree would look like this:
+
+      4
+     /
+    2
+
+If we then added 6, it would look like this:
+
+      4
+     / \
+    2   6
+
+If we then added 3, it would look like this
+
+       4
+     /   \
+    2     6
+     \
+      3
+
+And if we then added 1, 5, and 7, it would look like this
+
+          4
+        /   \
+       /     \
+      2       6
+     / \     / \
+    1   3   5   7
+
+## Resources
+
+- [Data structures: Binary Search Tree (YouTube)](https://youtu.be/pYT9F8_LFTM?t=9m39s)
+
+## Submitting Incomplete Solutions
+
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

exercises/binary-search-tree/analysis_options.yaml

@@ -0,0 +1,18 @@
+analyzer:
+  strong-mode:
+    implicit-casts: false
+    implicit-dynamic: false
+  errors:
+    unused_element:        error
+    unused_import:         error
+    unused_local_variable: error
+    dead_code:             error
+
+linter:
+  rules:
+      # Error Rules
+      - avoid_relative_lib_imports
+      - avoid_types_as_parameter_names
+      - literal_only_boolean_expressions
+      - no_adjacent_strings_in_list
+      - valid_regexps

exercises/binary-search-tree/lib/binary_search_tree.dart

@@ -0,0 +1,3 @@
+class BinarySearchTree {
+  // Put your code here
+}

exercises/binary-search-tree/lib/example.dart

@@ -0,0 +1,61 @@
+class BinarySearchTree<T extends Comparable<T>> {
+  /// Root node for the tree.
+  final Node<T> root;
+
+  BinarySearchTree(T rootData) : root = new Node<T>(rootData) {
+    // Note: [assert] does not run in release mode
+    assert(rootData != null);
+  }
+
+  /// Returns an empty `List` if [root] is `null`.
+  ///
+  /// Otherwise returns data traversed in ascending order.
+  Iterable<T> get sortedData sync* {
+    for (var t in root?.ascendingOrder ?? <T>[]) yield t;
+  }
+
+  /// Returns `true` on success, `false` on failure.
+  bool insert(T value) => root?.insert(value) ?? false;
+}
+
+class Node<T extends Comparable<T>> {
+  /// The actual Data this node holds which should be a [Comparable]
+  final T data;
+
+  /// Left node of this node, can be `null`
+  Node<T> left;
+
+  /// Right node of this node, can be `null`
+  Node<T> right;
+
+  Node(this.data, [this.left, this.right]) {
+    // Note: [assert] does not run in release mode
+    assert(data != null);
+  }
+
+  /// This is **inorder** traversal of the tree.
+  Iterable<T> get ascendingOrder sync* {
+    if (data == null) return;
+
+    /// Traverse left sub-tree if it's present
+    for (var t in left?.ascendingOrder ?? <T>[]) yield t;
+
+    yield data;
+
+    /// Traverse right sub-tree if it's present
+    for (var t in right?.ascendingOrder ?? <T>[]) yield t;
+  }
+
+  /// Returns `true` on success, `false` on failure.
+  bool insert(T value) {
+    if (value == null) return false;
+
+    /// Insert in left sub-tree if its a smaller or equal number.
+    if (value.compareTo(data) <= 0) {
+      return left?.insert(value) ?? (left = new Node(value)).data == value;
+    }
+
+    /// Insert in right sub-tree if its a greater number.
+    return right?.insert(value) ?? (right = new Node(value)).data == value;
+  }
+}

exercises/binary-search-tree/pubspec.yaml

@@ -0,0 +1,5 @@
+name: 'binary_search_tree'
+environment:
+  sdk: '>=1.24.0 <3.0.0'
+dev_dependencies:
+  test: '<2.0.0'

exercises/binary-search-tree/test/binary_search_tree_test.dart

@@ -0,0 +1,87 @@
+import 'package:binary_search_tree/binary_search_tree.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('BinarySearchTree', () {
+    test('data is retained', () {
+      final bst = new BinarySearchTree('4');
+
+      expect(bst.root.data, equals('4'));
+    }, skip: false);
+
+    group('insert data at proper node', () {
+      test('smaller number at left node', () {
+        final bst = new BinarySearchTree('4')..insert('2');
+
+        expect(bst.root.data, equals('4'));
+        expect(bst.root.left.data, equals('2'));
+      }, skip: true);
+
+      test('same number at left node', () {
+        final bst = new BinarySearchTree('4')..insert('4');
+
+        expect(bst.root.data, equals('4'));
+        expect(bst.root.left.data, equals('4'));
+      }, skip: true);
+
+      test('greater number at right node', () {
+        final bst = new BinarySearchTree('4')..insert('5');
+
+        expect(bst.root.data, equals('4'));
+        expect(bst.root.right.data, equals('5'));
+      }, skip: true);
+
+      test('can create complex tree', () {
+        final bst = new BinarySearchTree('4')
+          ..insert('2')
+          ..insert("6")
+          ..insert("1")
+          ..insert("3")
+          ..insert("5")
+          ..insert("7");
+
+        expect(bst.root.data, equals('4'));
+
+        expect(bst.root.left.data, equals('2'));
+        expect(bst.root.left.left.data, equals('1'));
+        expect(bst.root.left.right.data, equals('3'));
+
+        expect(bst.root.right.data, equals('6'));
+        expect(bst.root.right.left.data, equals('5'));
+        expect(bst.root.right.right.data, equals('7'));
+      }, skip: true);
+    });
+
+    group('can sort data', () {
+      test('can sort single number', () {
+        final bst = new BinarySearchTree('2');
+
+        expect(bst.sortedData, equals(['2']));
+      }, skip: true);
+
+      test('can sort if second number is smaller than first', () {
+        final bst = new BinarySearchTree('2')..insert('1');
+
+        expect(bst.sortedData, equals(['1', '2']));
+      }, skip: true);
+
+      test('can sort if second number is same as first', () {
+        final bst = new BinarySearchTree('2')..insert('2');
+
+        expect(bst.sortedData, equals(['2', '2']));
+      }, skip: true);
+
+      test('can sort if second number is greater than first', () {
+        final bst = new BinarySearchTree('2')..insert('3');
+
+        expect(bst.sortedData, equals(['2', '3']));
+      }, skip: true);
+
+      test('can sort complex tree', () {
+        final bst = new BinarySearchTree('2')..insert("1")..insert("3")..insert("6")..insert("7")..insert("5");
+
+        expect(bst.sortedData, equals(['1', '2', '3', '5', '6', '7']));
+      }, skip: true);
+    });
+  });
+}