feat(ctci): add p2.1 solution and unit tests

Author: Jessica Yung

laakmann-mcdowell/2-linked-lists/1_remove_duplicates.py

@@ -0,0 +1,91 @@
+"""
+2.1 Remove Duplicates
+
+Write code to remove duplicates from an unsorted linked list.
+
+How would you solve this problem if a temporary buffer is not allowed?
+
+Author: Jessica Yung
+15 October 2016
+"""
+import unittest
+
+
+class LinkedListNode(object):
+    """Singly Linked List Node"""
+
+    def __init__(self, value):
+        super(LinkedListNode, self).__init__()
+        self.value = value
+        self.next = None
+
+
+def remove_duplicates(first_node):
+    """
+    :type first_node: LinkedListNode
+    """
+
+    #
+    set_of_values = set()
+    previous_node = None
+    current_node = first_node
+    while current_node is not None:
+        # If duplicate
+        if current_node.value in set_of_values:
+            # Remove node
+            previous_node.next = current_node.next
+        else:
+            # If not duplicate, add value to set of values
+            set_of_values.add(current_node.value)
+            previous_node = current_node
+        # Move to next node: update previous and current nodes
+        current_node = current_node.next
+
+
+def remove_duplicates_no_temp_buffer(first_node):
+    current_node = first_node
+    while current_node is not None:
+        runner_node = current_node
+        while runner_node is not None:
+            if runner_node.next.value == current_node.value:
+                runner_node.next = runner_node.next.next
+            else:
+                runner_node = runner_node.next
+        current_node = current_node.next
+
+
+class Test(unittest.TestCase):
+    """Test"""
+
+    def set_up_linked_list(self):
+        a = LinkedListNode(1)
+        b = LinkedListNode(2)
+        c = LinkedListNode(3)
+        d = LinkedListNode(2)
+        e = LinkedListNode(4)
+        f = LinkedListNode(3)
+        g = LinkedListNode(5)
+        a.next = b
+        b.next = c
+        c.next = d
+        d.next = e
+        e.next = f
+        f.next = g
+        return a
+
+    def test_remove_duplicates(self):
+        a = self.set_up_linked_list()
+        remove_duplicates(a)
+        self.assertEqual(a, a)
+        self.assertEqual(a.next.value, 2)
+        self.assertEqual(a.next.next.next.value, 4)
+
+    def test_remove_duplicates_no_buffer(self):
+        a = self.set_up_linked_list()
+        remove_duplicates(a)
+        self.assertEqual(a, a)
+        self.assertEqual(a.next.value, 2)
+        self.assertEqual(a.next.next.next.value, 4)
+
+if __name__ == '__main__':
+    unittest.main()