Rock - Delia

linked_list/linked_list.py

@@ -13,105 +13,181 @@ 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
+        else: 
+            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(1)
     def add_first(self, value):
-        pass
+        new_node = Node(value)
+        new_node.next = self.head
+        self.head = new_node
 
     # 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
+        if not self.head:
+            return False
+        else:
+            curr_node = self.head
+            while curr_node != None:
+                if curr_node.value == value:
+                    return True
+                curr_node = curr_node.next
+            return False
 
     # 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
+        curr_node = self.head
+        len = 0
+        while curr_node != None:
+            len += 1
+            curr_node = curr_node.next
+        return len
 
     # 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
+        if index >= self.length():
+            print("The index is out of range")
+            return None
+        curr_index = 0
+        curr_node = self.head
+        while index > curr_index:
+            curr_node = curr_node.next
+            curr_index += 1
+        if curr_index == index:
+            return curr_node.value
 
     # 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
+        if not self.head:
+            return None
+        curr_node = self.head
+        while curr_node.next != None:
+            curr_node = curr_node.next
+        return curr_node.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_node = Node(value)
+        if not self.head:
+            self.head = new_node
+            return
+        curr_node = self.head
+        while curr_node.next != None:
+            curr_node = curr_node.next
+        curr_node.next = new_node
 
     # method to return the max value in the linked list
     # returns the data value and not the node
     def find_max(self):
-        pass
+        if not self.head:
+            return None
+        curr_node = self.head
+        max_value = self.head.value
+        while curr_node != None:
+            if curr_node.value > max_value:
+                max_value = curr_node.value
+            curr_node = curr_node.next
+        return max_value
 
     # method to delete the first node found with specified value
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def delete(self, value):
-        pass
+        if not self.head:
+            return None
+        curr_node = self.head
+        if value == curr_node.value:
+            self.head = curr_node.next
+            return
+        while curr_node != None:
+            prev_node = curr_node
+            curr_node = curr_node.next
+            if value == curr_node.value:
+                prev_node.next = curr_node.next
+                return 
 
     # 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
+        curr_node = self.head
 
-        while current:
-            helper_list.append(str(current.value))
-            current = current.next
+        while curr_node:
+            helper_list.append(str(curr_node.value))
+            curr_node = curr_node.next
 
         print(", ".join(helper_list))
+        return 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(n)
     def reverse(self):
-        pass
+        prev_node = None
+        curr_node = self.head
+        while curr_node != None:
+            next_node = curr_node.next
+            curr_node.next = prev_node
+            prev_node = curr_node
+            curr_node = next_node
+        self.head = prev_node
 
     ## 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
+        len_list = self.length()
+        index = len_list // 2
+        return self.get_at_index(index)
 
     # 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
+        len_list = self.length()
+        index = len_list - 1 - n
+        return self.get_at_index(index)
 
     # 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(1)
     def has_cycle(self):
-        pass
+        slow_p = self.head
+        fast_p = self.head
+        while fast_p and fast_p.next != None:
+            slow_p = slow_p.next
+            fast_p = fast_p.next.next
+            if slow_p == fast_p:
+                return True
+        return False
 
     # Helper method for tests
     # Creates a cycle in the linked list for testing purposes
@@ -121,8 +197,9 @@ def create_cycle(self):
             return
 
         # navigate to last node
-        current = self.head
-        while current.next != None:
-            current = current.next
+        curr_node = self.head
+        while curr_node.next != None:
+            curr_node = curr_node.next
+
+        curr_node.next = self.head # make the last node link to first node
 
-        current.next = self.head # make the last node link to first node

tests/linked_list_test.py

@@ -192,12 +192,11 @@ def test_reverse_will_reverse_five_element_list(list):
     for i in range(0, 5):
         list.add_first(i)
 
-    list.reverse()
+    list.reverse() 
 
     for i in range(0, 5):
         assert list.get_at_index(i) == i
 
-@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 +205,6 @@ 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")
 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 +214,9 @@ 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")
 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")
 def test_find_nth_from_n_when_length_less_than_n(list):
     list.add_first(5)
     list.add_first(4)
@@ -230,7 +226,6 @@ 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")
 def test_find_nth_from_n(list):
     list.add_first(1)
     list.add_first(2)
@@ -243,7 +238,6 @@ 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")
 def test_has_cycle(list):
     assert list.has_cycle() == False