Adriana Gutierrez - SeaTurtles - C17

binary_search_trees/array_to_bst.py

@@ -10,4 +10,64 @@ def arr_to_bst(arr):
         Balanced Binary Search Tree using the elements in the array.
         Return the root of the Binary Search Tree.
     """
-    pass
+    def returnOddVals(arr):
+        mid_index = len(arr)//2
+        return arr[mid_index], arr[:mid_index], arr[mid_index+1:]
+
+    def returnEvenVals(arr):
+        mid_index = len(arr)//2-1
+        return arr[mid_index], arr[:mid_index], arr[mid_index+1:]
+
+    def recursive_helper(prev, left_side, right_side):
+        if not prev:
+            return None
+        #left side
+        if not left_side:
+            new_node_val = None
+        elif len(left_side) == 1:
+            new_node_val = left_side[0]
+            new_left_node = TreeNode(new_node_val)
+            prev.left = new_left_node
+        else:
+            if len(left_side)%2 == 0:
+                new_node_val, new_left_for_left_side, new_right_for_left_side = returnEvenVals(left_side)
+            else:
+                new_node_val, new_left_for_left_side, new_right_for_left_side = returnOddVals(left_side)
+            if new_node_val != None:
+                new_left_node = TreeNode(new_node_val)
+            else:
+                new_left_node = None
+            prev.left = new_left_node
+            recursive_helper(new_left_node, new_left_for_left_side, new_right_for_left_side)
+
+        #right side
+        if not right_side:
+            new_node_val = None
+        elif len(right_side) == 1:
+            new_node_val = right_side[0]
+            new_right_node = TreeNode(new_node_val)
+            prev.right = new_right_node
+        else:
+            if len(right_side)%2 == 0:
+                new_node_val, new_left_for_right_side, new_right_for_right_side = returnEvenVals(right_side)
+            else:
+                new_node_val, new_left_for_right_side, new_right_for_right_side = returnOddVals(right_side)
+            if new_node_val != None:
+                new_right_node = TreeNode(new_node_val)
+            else:
+                new_right_node = None
+            prev.right = new_right_node
+            recursive_helper(new_right_node, new_left_for_right_side, new_right_for_right_side)
+
+    if not arr:
+        return None
+    if len(arr) == 1:
+        root = TreeNode(arr[0])
+    else:
+        if len(arr)%2 == 0:
+            root_val, left_side, right_side = returnEvenVals(arr)
+        else:
+            root_val, left_side, right_side = returnOddVals(arr)
+        root = TreeNode(root_val)
+        recursive_helper(root, left_side, right_side)
+    return root