Changed discussions of NULL to None to be more Pythonic.

arrays_strings/hash_map/hash_map_solution.ipynb

@@ -85,7 +85,7 @@
     "\n",
     "* Get hash index for lookup\n",
     "* If key exists, return value\n",
-    "* Else, return NULL\n",
+    "* Else, return None\n",
     "\n",
     "Complexity:\n",
     "* Time: O(1) average and best, O(n) worst\n",

linked_lists/add_reverse/add_reverse_solution.ipynb

@@ -70,8 +70,8 @@
     "We could solve this with an iterative or a recursive algorithm, both are well suited for this exercise.  We'll use a recursive algorithm for practice with recursion.  Note this takes an extra space of O(m) where m is the recursion depth.\n",
     "\n",
     "* Base case:\n",
-    "    * if first and second lists are NULL AND carry is zero\n",
+    "    * if first and second lists are None AND carry is zero\n",
-    "        * Return NULL\n",
+    "        * Return None\n",
     "* Recursive case:\n",
     "    * Set `value` to `carry`\n",
     "    * Add both nodes' `data` to `value`\n",
@@ -87,7 +87,7 @@
     "\n",
     "Notes:\n",
     "* Careful with adding if the lists differ\n",
-    "    * Only add if a node is not NULL\n",
+    "    * Only add if a node is not None\n",
     "    * Alternatively, we could add trailing zeroes to the smaller list"
    ]
   },

linked_lists/delete_mid/delete_mid_challenge.ipynb

@@ -36,7 +36,7 @@
     "\n",
     "*Problem statements are sometimes ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
     "\n",
-    "* What if the final node is being deleted, for example a single node list?  Do we make it a dummy with a NULL value?\n",
+    "* What if the final node is being deleted, for example a single node list?  Do we make it a dummy with value None?\n",
     "    * Yes\n",
     "* Can we assume we already have a linked list class that can be used for this problem?\n",
     "    * Yes"

linked_lists/delete_mid/delete_mid_solution.ipynb

@@ -35,7 +35,7 @@
     "\n",
     "*Problem statements are sometimes ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
     "\n",
-    "* What if the final node is being deleted, for example a single node list?  Do we make it a dummy with a NULL value?\n",
+    "* What if the final node is being deleted, for example a single node list?  Do we make it a dummy with value None?\n",
     "    * Yes\n",
     "* Can we assume we already have a linked list class that can be used for this problem?\n",
     "    * Yes"

linked_lists/linked_list/linked_list_challenge.ipynb

@@ -52,26 +52,26 @@
     "\n",
     "### Insert to Front\n",
     "\n",
-    "* Insert a NULL\n",
+    "* Insert a None\n",
     "* Insert in an empty list\n",
     "* Insert in a list with one element or more elements\n",
     "\n",
     "### Append\n",
     "\n",
-    "* Append a NULL\n",
+    "* Append a None\n",
     "* Append in an empty list\n",
     "* Insert in a list with one element or more elements\n",
     "\n",
     "### Find\n",
     "\n",
-    "* Find a NULL\n",
+    "* Find a None\n",
     "* Find in an empty list\n",
     "* Find in a list with one element or more matching elements\n",
     "* Find in a list with no matches\n",
     "\n",
     "### Delete\n",
     "\n",
-    "* Delete a NULL\n",
+    "* Delete a None\n",
     "* Delete in an empty list\n",
     "* Delete in a list with one element or more matching elements\n",
     "* Delete in a list with no matches\n",
@@ -191,7 +191,7 @@
     "        linked_list.insert_to_front(10)\n",
     "        assert_equal(linked_list.get_all_data(), [10])\n",
     "\n",
-    "        print('Test: insert_to_front on a NULL')\n",
+    "        print('Test: insert_to_front on a None')\n",
     "        linked_list.insert_to_front(None)\n",
     "        assert_equal(linked_list.get_all_data(), [10])\n",
     "\n",
@@ -208,7 +208,7 @@
     "        linked_list.append(10)\n",
     "        assert_equal(linked_list.get_all_data(), [10])\n",
     "\n",
-    "        print('Test: append a NULL')\n",
+    "        print('Test: append a None')\n",
     "        linked_list.append(None)\n",
     "        assert_equal(linked_list.get_all_data(), [10])\n",
     "\n",
@@ -225,7 +225,7 @@
     "        node = linked_list.find('a')\n",
     "        assert_equal(node, None)\n",
     "\n",
-    "        print('Test: find a NULL')\n",
+    "        print('Test: find a None')\n",
     "        head = Node(10)\n",
     "        linked_list = LinkedList(head)\n",
     "        node = linked_list.find(None)\n",
@@ -251,7 +251,7 @@
     "        linked_list.delete('a')\n",
     "        assert_equal(linked_list.get_all_data(), [])\n",
     "\n",
-    "        print('Test: delete a NULL')\n",
+    "        print('Test: delete a None')\n",
     "        head = Node(10)\n",
     "        linked_list = LinkedList(head)\n",
     "        linked_list.delete(None)\n",

linked_lists/linked_list/linked_list_solution.ipynb

@@ -51,26 +51,26 @@
     "\n",
     "### Insert to Front\n",
     "\n",
-    "* Insert a NULL\n",
+    "* Insert a None\n",
     "* Insert in an empty list\n",
     "* Insert in a list with one element or more elements\n",
     "\n",
     "### Append\n",
     "\n",
-    "* Append a NULL\n",
+    "* Append a None\n",
     "* Append in an empty list\n",
     "* Insert in a list with one element or more elements\n",
     "\n",
     "### Find\n",
     "\n",
-    "* Find a NULL\n",
+    "* Find a None\n",
     "* Find in an empty list\n",
     "* Find in a list with one element or more matching elements\n",
     "* Find in a list with no matches\n",
     "\n",
     "### Delete\n",
     "\n",
-    "* Delete a NULL\n",
+    "* Delete a None\n",
     "* Delete in an empty list\n",
     "* Delete in a list with one element or more matching elements\n",
     "* Delete in a list with no matches\n",
@@ -93,7 +93,7 @@
     "\n",
     "### Insert to Front\n",
     "\n",
-    "* If the data we are inserting is NULL, return\n",
+    "* If the data we are inserting is None, return\n",
     "* Create a node with the input data\n",
     "* If this is an empty list\n",
     "    * Assign the head to the node\n",
@@ -107,7 +107,7 @@
     "\n",
     "### Append\n",
     "\n",
-    "* If the data we are inserting is NULL, return\n",
+    "* If the data we are inserting is None, return\n",
     "* Create a node with the input data\n",
     "* If this is an empty list\n",
     "    * Assign the head to the node\n",
@@ -121,7 +121,7 @@
     "\n",
     "### Find\n",
     "\n",
-    "* If data we are finding is NULL, return\n",
+    "* If data we are finding is None, return\n",
     "* If the list is empty, return\n",
     "* For each node\n",
     "    * If the value is a match, return it\n",
@@ -133,7 +133,7 @@
     "\n",
     "### Delete\n",
     "\n",
-    "* If data we are deleting is NULL, return\n",
+    "* If data we are deleting is None, return\n",
     "* If the list is empty, return\n",
     "* For each node, keep track of previous and current node\n",
     "    * If the value we are deleting is a match in the current node\n",
@@ -323,7 +323,7 @@
     "        linked_list.insert_to_front(10)\n",
     "        assert_equal(linked_list.get_all_data(), [10])\n",
     "\n",
-    "        print('Test: insert_to_front on a NULL')\n",
+    "        print('Test: insert_to_front on a None')\n",
     "        linked_list.insert_to_front(None)\n",
     "        assert_equal(linked_list.get_all_data(), [10])\n",
     "\n",
@@ -340,7 +340,7 @@
     "        linked_list.append(10)\n",
     "        assert_equal(linked_list.get_all_data(), [10])\n",
     "\n",
-    "        print('Test: append a NULL')\n",
+    "        print('Test: append a None')\n",
     "        linked_list.append(None)\n",
     "        assert_equal(linked_list.get_all_data(), [10])\n",
     "\n",
@@ -357,7 +357,7 @@
     "        node = linked_list.find('a')\n",
     "        assert_equal(node, None)\n",
     "\n",
-    "        print('Test: find a NULL')\n",
+    "        print('Test: find a None')\n",
     "        head = Node(10)\n",
     "        linked_list = LinkedList(head)\n",
     "        node = linked_list.find(None)\n",
@@ -383,7 +383,7 @@
     "        linked_list.delete('a')\n",
     "        assert_equal(linked_list.get_all_data(), [])\n",
     "\n",
-    "        print('Test: delete a NULL')\n",
+    "        print('Test: delete a None')\n",
     "        head = Node(10)\n",
     "        linked_list = LinkedList(head)\n",
     "        linked_list.delete(None)\n",
@@ -441,23 +441,23 @@
      "output_type": "stream",
      "text": [
       "Test: insert_to_front on an empty list\n",
-      "Test: insert_to_front on a NULL\n",
+      "Test: insert_to_front on a None\n",
       "Test: insert_to_front general case\n",
       "Success: test_insert_to_front\n",
       "\n",
       "Test: append on an empty list\n",
-      "Test: append a NULL\n",
+      "Test: append a None\n",
       "Test: append general case\n",
       "Success: test_append\n",
       "\n",
       "Test: find on an empty list\n",
-      "Test: find a NULL\n",
+      "Test: find a None\n",
       "Test: find general case with matches\n",
       "Test: find general case with no matches\n",
       "Success: test_find\n",
       "\n",
       "Test: delete on an empty list\n",
-      "Test: delete a NULL\n",
+      "Test: delete a None\n",
       "Test: delete general case with matches\n",
       "Test: delete general case with no matches\n",
       "Success: test_delete\n",

linked_lists/linked_list/test_linked_list.py

@@ -2,14 +2,14 @@ from nose.tools import assert_equal
 
 
 class TestLinkedList(object):
-    
+
     def test_insert_to_front(self):
         print('Test: insert_to_front on an empty list')
         linked_list = LinkedList(None)
         linked_list.insert_to_front(10)
         assert_equal(linked_list.get_all_data(), [10])
 
-        print('Test: insert_to_front on a NULL')
+        print('Test: insert_to_front on a None')
         linked_list.insert_to_front(None)
         assert_equal(linked_list.get_all_data(), [10])
 
@@ -17,16 +17,16 @@ class TestLinkedList(object):
         linked_list.insert_to_front('a')
         linked_list.insert_to_front('bc')
         assert_equal(linked_list.get_all_data(), ['bc', 'a', 10])
-        
+
         print('Success: test_insert_to_front\n')
-        
+
     def test_append(self):
         print('Test: append on an empty list')
         linked_list = LinkedList(None)
         linked_list.append(10)
         assert_equal(linked_list.get_all_data(), [10])
 
-        print('Test: append a NULL')
+        print('Test: append a None')
         linked_list.append(None)
         assert_equal(linked_list.get_all_data(), [10])
 
@@ -34,16 +34,16 @@ class TestLinkedList(object):
         linked_list.append('a')
         linked_list.append('bc')
         assert_equal(linked_list.get_all_data(), [10, 'a', 'bc'])
-        
+
         print('Success: test_append\n')
-        
+
     def test_find(self):
         print('Test: find on an empty list')
         linked_list = LinkedList(None)
         node = linked_list.find('a')
         assert_equal(node, None)
 
-        print('Test: find a NULL')
+        print('Test: find a None')
         head = Node(10)
         linked_list = LinkedList(head)
         node = linked_list.find(None)
@@ -60,16 +60,16 @@ class TestLinkedList(object):
         print('Test: find general case with no matches')
         node = linked_list.find('aaa')
         assert_equal(node, None)
-        
+
         print('Success: test_find\n')
-        
+
     def test_delete(self):
         print('Test: delete on an empty list')
         linked_list = LinkedList(None)
         linked_list.delete('a')
         assert_equal(linked_list.get_all_data(), [])
 
-        print('Test: delete a NULL')
+        print('Test: delete a None')
         head = Node(10)
         linked_list = LinkedList(head)
         linked_list.delete(None)
@@ -86,9 +86,9 @@ class TestLinkedList(object):
         print('Test: delete general case with no matches')
         linked_list.delete('aa')
         assert_equal(linked_list.get_all_data(), ['bc', 10])
-        
+
         print('Success: test_delete\n')
-        
+
     def test_len(self):
         print('Test: len on an empty list')
         linked_list = LinkedList(None)
@@ -100,7 +100,7 @@ class TestLinkedList(object):
         linked_list.insert_to_front('a')
         linked_list.insert_to_front('bc')
         assert_equal(len(linked_list), 3)
-        
+
         print('Success: test_len\n')
 
 def main():
@@ -110,6 +110,6 @@ def main():
     test.test_find()
     test.test_delete()
     test.test_len()
-    
+
 if __name__ == '__main__':
     main()

stacks_queues/hanoi/hanoi_challenge.ipynb

@@ -46,7 +46,7 @@
    "source": [
     "## Test Cases\n",
     "\n",
-    "* NULL tower(s)\n",
+    "* None tower(s)\n",
     "* 0 disks\n",
     "* 1 disk\n",
     "* 2 or more disks"
@@ -124,7 +124,7 @@
     "        buff = Stack()\n",
     "        dest = Stack()\n",
     "\n",
-    "        print('Test: NULL towers')\n",
+    "        print('Test: None towers')\n",
     "        hanoi(num_disks, None, None, None)\n",
     "\n",
     "        print('Test: 0 disks')\n",

stacks_queues/hanoi/hanoi_solution.ipynb

@@ -45,7 +45,7 @@
    "source": [
     "## Test Cases\n",
     "\n",
-    "* NULL tower(s)\n",
+    "* None tower(s)\n",
     "* 0 disks\n",
     "* 1 disk\n",
     "* 2 or more disks"
@@ -141,7 +141,7 @@
     "        buff = Stack()\n",
     "        dest = Stack()\n",
     "\n",
-    "        print('Test: NULL towers')\n",
+    "        print('Test: None towers')\n",
     "        hanoi(num_disks, None, None, None)\n",
     "\n",
     "        print('Test: 0 disks')\n",
@@ -181,7 +181,7 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "Test: NULL towers\n",
+      "Test: None towers\n",
       "Test: 0 disks\n",
       "Test: 1 disk\n",
       "Test: 2 or more disks\n",

stacks_queues/hanoi/test_hanoi.py

@@ -2,14 +2,14 @@ from nose.tools import assert_equal
 
 
 class TestHanoi(object):
-    
+
     def test_hanoi(self):
         num_disks = 3
         src = Stack()
         buff = Stack()
         dest = Stack()
 
-        print('Test: NULL towers')
+        print('Test: None towers')
         hanoi(num_disks, None, None, None)
 
         print('Test: 0 disks')
@@ -33,6 +33,6 @@ class TestHanoi(object):
 def main():
     test = TestHanoi()
     test.test_hanoi()
-    
+
 if __name__ == '__main__':
     main()

stacks_queues/stack/stack_solution.ipynb

@@ -85,7 +85,7 @@
     "\n",
     "### Pop\n",
     "\n",
-    "* If stack is empty, return NULL\n",
+    "* If stack is empty, return None\n",
     "* Else \n",
     "    * Save top's value\n",
     "    * Set top to top.next\n",
@@ -97,7 +97,7 @@
     "\n",
     "### Peek\n",
     "\n",
-    "* If stack is empty, return NULL\n",
+    "* If stack is empty, return None\n",
     "* Else return top's value\n",
     "\n",
     "Complexity:\n",