diff --git a/linked_list/linked_list.py b/linked_list/linked_list.py index 63993214..d5d92e62 100644 --- a/linked_list/linked_list.py +++ b/linked_list/linked_list.py @@ -16,80 +16,142 @@ def __init__(self): # Time Complexity: ? # Space Complexity: ? def get_first(self): - pass + if self.head == None: + 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 + 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 + current = self.head + while current != None: + if current.value == value: + return True + current = current.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 + counter = 0 + current = self.head + while current != None: + current = current.next + counter += 1 + return counter # 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 self.length() < index: + return None + current = self.head + current_index = 0 + while current != None: + if current_index == index: + return current.value + current = current.next + current_index += 1 # 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 self.head == None: + return None + current = self.head + while current.next != None: + 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_node = Node(value) + if self.head == None: + self.head = new_node + return + current = self.head + while current.next != None: + current = current.next + current.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 self.head == None: + return None + max_value = self.head.value + current = self.head.next + while current != None: + if max_value < current.value: + max_value = current.value + current = current.next + return max_value # method to delete the first node found with specified value - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(1) + # Space Complexity: O(n) def delete(self, value): - pass + curr = self.head + prev = None + if curr == None: + return None + while curr: + if curr.value == value: + # if not head of list + if prev: + prev.next = curr.next + else: + self.head = curr.next + prev = curr + curr = curr.next # 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 + prev = None + current = self.head + next = None + + while current != None: + next = current.next + current.next = prev + prev = current + current = next + self.head = prev ## Advanced/ Exercises # returns the value at the middle element in the singly linked list