scissors laurel O

linked_list/linked_list.py

@@ -13,105 +13,199 @@ def __init__(self):
 
     # returns the value in the first node
     # returns None if the list is empty
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(1)
+    # Space Complexity: O(1)
     def get_first(self):
-        pass
+        if self.head:
+            return self.head.value
+        return None
 
 
     # method to add a new node with the specific data value in the linked list
     # insert the new node at the beginning of the linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(1)
+    # Space Complexity: O(n)
     def add_first(self, value):
-        pass
+        new_first = Node(value, self.head)
+        new_first.next_node = self.head
+        self.head = new_first
+
 
     # method to find if the linked list contains a node with specified value
     # returns true if found, false otherwise
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def search(self, value):
-        pass
+        current = self.head
+        found = False
+        while found is False and current is not None:
+            if current.value == value:
+                found = True
+            else:
+                current = current.next
+        return found
+
 
     # method that returns the length of the singly linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def length(self):
-        pass
+        current = self.head
+        length = 0
+        while current:
+            length += 1
+            current = current.next
+        return length
+
 
     # method that returns the value at a given index in the linked list
-    # index count starts at 0
     # returns None if there are fewer nodes in the linked list than the index value
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def get_at_index(self, index):
-        pass
+        current = self.head
+        i = 0
+        while i < index and current is not None:
+            i += 1
+            current = current.next
+        if i == index:
+            return current.value
+        return None
+
 
     # method that returns the value of the last node in the linked list
     # returns None if the linked list is empty
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def get_last(self):
-        pass
+        current = self.head
+        if not current:
+            return None
+        while current.next:
+            current = current.next
+        return current.value
 
     # method that inserts a given value as a new last node in the linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def add_last(self, value):
-        pass
+        new_last = Node(value)
+        if self.head is None:
+            self.head = new_last
+            return
+        else:
+            current = self.head
+            while current.next is not None:
+                current = current.next
+            current.next = new_last
+
 
     # method to return the max value in the linked list
     # returns the data value and not the node
     def find_max(self):
-        pass
+        current = self.head
+        if current is None:
+            return None
+        max = current.value
+        while current:
+            if max < current.value:
+                max = current.value
+            current = current.next
+        return max
+
 
     # method to delete the first node found with specified value
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # (should be able to be done in O(1) if just getting rid of pointer?)
+    # Space Complexity: O(1)
     def delete(self, value):
-        pass
+        current = self.head
+        if current:
+            if current.value == value:
+                self.head = current.next
+                current = None
+                return
+        while current:
+            if current.value == value:
+                break
+            previous = current
+            current = current.next
+        if current == None:
+            return
+        previous.next = current.next
+        current = None
+
 
     # method to print all the values in the linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(n)
     def visit(self):
         helper_list = []
         current = self.head
-
         while current:
             helper_list.append(str(current.value))
             current = current.next
-
         print(", ".join(helper_list))
 
+
     # method to reverse the singly linked list
     # note: the nodes should be moved and not just the values in the nodes
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def reverse(self):
-        pass
+        previous = None
+        current = self.head
+        while current is not None:
+            next = current.next
+            current.next = previous
+            previous = current
+            current = next
+        self.head = previous
 
+
     ## Advanced/ Exercises
     # returns the value at the middle element in the singly linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def find_middle_value(self):
-        pass
+        if not self.head:
+            return None
+
+        return self.get_at_index(int(self.length()/2))
+
 
     # find the nth node from the end and return its value
     # assume indexing starts at 0 while counting to n
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def find_nth_from_end(self, n):
-        pass
+        current = self.head
+        if not current:
+            return None
+        len = self.length() - 1
+        if n > len:
+            return
+        for i in range(0, len - n):
+            current = current.next
+        return current.value
+
 
     # checks if the linked list has a cycle. A cycle exists if any node in the
     # linked list links to a node already visited.
     # returns true if a cycle is found, false otherwise.
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(n)
     def has_cycle(self):
-        pass
+        current = self.head
+        visited = set()
+        if current == None:
+            return False
+        while current.next != None:
+            visited.add(current)
+            current = current.next
+            if current in visited:
+                return True
+        return False
 
     # Helper method for tests
     # Creates a cycle in the linked list for testing purposes

tests/linked_list_test.py

@@ -197,7 +197,7 @@ def test_reverse_will_reverse_five_element_list(list):
     for i in range(0, 5):
         assert list.get_at_index(i) == i
 
-@pytest.mark.skip(reason="Going Further methods")
+#@pytest.mark.skip(reason="Going Further methods")
 def test_find_middle_value_returns_middle_element_of_five_element_list(list):
     list.add_first(10)
     list.add_first(30)
@@ -206,7 +206,7 @@ def test_find_middle_value_returns_middle_element_of_five_element_list(list):
     list.add_first(20)
     assert list.find_middle_value() == 50
 
-@pytest.mark.skip(reason="Going Further methods")
+#@pytest.mark.skip(reason="Going Further methods")
 def test_find_middle_value_returns_element_at_index_two_of_six_element_list(list):
     list.add_first(10)
     list.add_first(30)
@@ -216,11 +216,11 @@ def test_find_middle_value_returns_element_at_index_two_of_six_element_list(list
     list.add_first(100)
     assert list.find_middle_value() == 60
 
-@pytest.mark.skip(reason="Going Further methods")
+#@pytest.mark.skip(reason="Going Further methods")
 def test_nth_from_n_when_list_is_empty(list):
     assert list.find_nth_from_end(3) == None
 
-@pytest.mark.skip(reason="Going Further methods")
+#@pytest.mark.skip(reason="Going Further methods")
 def test_find_nth_from_n_when_length_less_than_n(list):
     list.add_first(5)
     list.add_first(4)
@@ -230,7 +230,7 @@ def test_find_nth_from_n_when_length_less_than_n(list):
 
     assert list.find_nth_from_end(6) == None
 
-@pytest.mark.skip(reason="Going Further methods")
+#@pytest.mark.skip(reason="Going Further methods")
 def test_find_nth_from_n(list):
     list.add_first(1)
     list.add_first(2)
@@ -243,7 +243,7 @@ def test_find_nth_from_n(list):
     assert list.find_nth_from_end(3) ==  4
     assert list.find_nth_from_end(4) ==  None
 
-@pytest.mark.skip(reason="Going Further methods")
+#@pytest.mark.skip(reason="Going Further methods")
 def test_has_cycle(list):
     assert list.has_cycle() == False