Implement exercise binary-search-tree (#773)

config.json

@@ -1200,6 +1200,20 @@
         "reactive_programming"
       ]
     },
+    {
+      "uuid": "6f196341-0ffc-9780-a7ca-1f817508247161cbcd9",
+      "slug": "binary-search-tree",
+      "core": false,
+      "unlocked_by": null,
+      "difficulty": 4,
+      "topics":[
+        "recursion",
+        "classes",
+        "trees",
+        "searching",
+        "object_oriented_programming"
+      ]
+    },
     {
       "uuid": "e7351e8e-d3ff-4621-b818-cd55cf05bffd",
       "slug": "accumulate",

exercises/binary-search-tree/README.md

@@ -0,0 +1,71 @@
+# 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
+
+
+## Submitting Exercises
+
+Note that, when trying to submit an exercise, make sure the solution is in the `exercism/python/<exerciseName>` directory.
+
+For example, if you're submitting `bob.py` for the Bob exercise, the submit command would be something like `exercism submit <path_to_exercism_dir>/python/bob/bob.py`.
+
+For more detailed information about running tests, code style and linting,
+please see the [help page](http://exercism.io/languages/python).
+
+## Source
+
+Wikipedia [https://en.wikipedia.org/wiki/Binary_search_tree](https://en.wikipedia.org/wiki/Binary_search_tree)
+
+## 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/binary_search_tree.py

@@ -0,0 +1,14 @@
+class TreeNode(object):
+    def __init__(self, value):
+        self.value = value
+
+
+class BinarySearchTree(object):
+    def __init__(self):
+        pass
+
+    def add(self, value):
+        pass
+
+    def search(self, value):
+        pass

exercises/binary-search-tree/binary_search_tree_test.py

@@ -0,0 +1,58 @@
+import unittest
+
+from binary_search_tree import BinarySearchTree
+
+
+class BinarySearchTreeTests(unittest.TestCase):
+
+    def test_add_integer_numbers(self):
+        bst = BinarySearchTree()
+        bst.add(1)
+        bst.add(8)
+        bst.add(3)
+        bst.add(5)
+        bst.add(2)
+        self.assertEqual(list(bst.list()), [1, 2, 3, 5, 8])
+
+    def test_add_float_numbers(self):
+        bst = BinarySearchTree()
+        bst.add(7.5)
+        bst.add(5.3)
+        bst.add(5.5)
+        bst.add(6.0)
+        bst.add(7.7)
+        self.assertEqual(list(bst.list()), [5.3, 5.5, 6.0, 7.5, 7.7])
+
+    def test_add_mixed_numbers(self):
+        bst = BinarySearchTree()
+        bst.add(1)
+        bst.add(8)
+        bst.add(7.5)
+        bst.add(5.3)
+        self.assertEqual(list(bst.list()), [1, 5.3, 7.5, 8])
+
+    def test_add_duplicated_numbers(self):
+        bst = BinarySearchTree()
+        bst.add(1)
+        bst.add(1)
+        bst.add(7.5)
+        bst.add(5.3)
+        self.assertEqual(list(bst.list()), [1, 1, 5.3, 7.5])
+
+    def test_search_existent_numbers(self):
+        bst = BinarySearchTree()
+        bst.add(1)
+        bst.add(7.5)
+        self.assertEqual(bst.search(1).value, 1)
+        self.assertEqual(bst.search(7.5).value, 7.5)
+
+    def test_search_nonexistent_numbers(self):
+        bst = BinarySearchTree()
+        bst.add(1)
+        bst.add(7.5)
+        self.assertIs(bst.search(6), None)
+        self.assertIs(bst.search(8.8), None)
+
+
+if __name__ == '__main__':
+    unittest.main()

exercises/binary-search-tree/example.py

@@ -0,0 +1,61 @@
+from collections import deque
+
+
+class TreeNode(object):
+    def __init__(self, value):
+        self.value = value
+        self.left_node = None
+        self.right_node = None
+
+    def __str__(self):
+        return str(self.value)
+
+
+class BinarySearchTree(object):
+    def __init__(self):
+        self.root = None
+
+    def add(self, value):
+        if(self.root is None):
+            self.root = TreeNode(value)
+        else:
+            inserted = False
+            cur_node = self.root
+
+            while not inserted:
+                if(value <= cur_node.value):
+                    if(cur_node.left_node):
+                        cur_node = cur_node.left_node
+                    else:
+                        cur_node.left_node = TreeNode(value)
+                        inserted = True
+                elif(value > cur_node.value):
+                    if(cur_node.right_node):
+                        cur_node = cur_node.right_node
+                    else:
+                        cur_node.right_node = TreeNode(value)
+                        inserted = True
+
+    def search(self, value):
+        cur_node = self.root
+        found = False
+        while not found:
+            if(cur_node is None):
+                return None
+            elif(value < cur_node.value):
+                cur_node = cur_node.left_node
+            elif(value > cur_node.value):
+                cur_node = cur_node.right_node
+            elif(value == cur_node.value):
+                return cur_node
+
+    def list(self):
+        elements = deque()
+        self.trav_inorder(self.root, elements)
+        return elements
+
+    def trav_inorder(self, node, elements):
+        if(node is not None):
+            self.trav_inorder(node.left_node, elements)
+            elements.append(node.value)
+            self.trav_inorder(node.right_node, elements)