Alf (Asli) - Spruce - C16

linked_list/linked_list.py

@@ -9,67 +9,124 @@ def __init__(self, value, next_node = None):
 # Defines the singly linked list
 class LinkedList:
     def __init__(self):
-      self.head = None # keep the head private. Not accessible outside this class
+        self.head = None # keep the head private. Not accessible outside this class
 
     # 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 not self.head:
+            return None
+
+        return self.head.value
 
 
     # 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
+        added = Node(value)
+        added.next = self.head
+        self.head = added
 
     # 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
+        curr = self.head
+        while curr:
+            if curr.value == value:
+                return True
+            curr = curr.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
+        len = 0
+        curr = self.head
+        while curr:
+            len += 1
+            curr = curr.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
+        i = 0
+        curr = self.head
+        while curr:
+            if i == index:
+                return curr.value
+            i += 1
+            curr = curr.next
+
+        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
+        if not self.head:
+            return None
+        curr = self.head
+        while curr.next:
+            curr = curr.next
+        return curr.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
+        if not self.head:
+            self.head = Node(value)
+            return
+        curr = self.head
+        while curr.next:
+            curr = curr.next
+        curr.next = Node(value)
 
     # method to return the max value in the linked list
     # returns the data value and not the node
+    #Time Complexity: O(n)
+    #Space Complexity: O(1)
     def find_max(self):
-        pass
+        max = 0
+        if not self.head:
+            return None
+        curr = self.head
+        while curr:
+            if curr.value > max:
+                max = curr.value
+            curr = curr.next
+        return max
 
     # 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
+        curr = self.head
+        prev = None
+        if not curr:
+            return None
+        if curr.value == value:
+            self.head = curr.next
+            return 
+        while curr:
+            if curr.value == value:
+                prev.next = curr.next
+                return
+            prev = curr
+            curr = curr.next
 
     # method to print all the values in the linked list
     # Time Complexity: ?
@@ -86,32 +143,60 @@ def visit(self):
 
     # 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
-
+        if not self.head or not self.head.next:
+            return
+        if self.length() == 2:
+            second = self.head.next
+            self.head.next = None
+            second.next = self.head
+            self.head = second
+            return
+
+        prev = self.head
+        curr = self.head.next
+        next = curr.next
+        while next:
+            curr.next = prev
+            prev = curr
+            curr = next
+            next = next.next
+        curr.next = prev
+        self.head.next = None
+        self.head = curr
+
     ## 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
+        mid = self.length() // 2
+        return self.get_at_index(mid)
 
     # 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 = self.length()
+        return self.get_at_index(len - 1 - n)
 
     # 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
+        node_map = {}
+        curr = self.head
+        while curr:
+            if node_map.get(curr):
+                return True
+            node_map[curr] = True
+            curr = curr.next
+        return False
 
     # Helper method for tests
     # Creates a cycle in the linked list for testing purposes

tests/linked_list_test.py

@@ -197,7 +197,6 @@ 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")
 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 +238,7 @@ 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")
+
 def test_has_cycle(list):
     assert list.has_cycle() == False