diff --git a/linked_list/linked_list.py b/linked_list/linked_list.py index 63993214..0ebca9fc 100644 --- a/linked_list/linked_list.py +++ b/linked_list/linked_list.py @@ -13,67 +13,135 @@ 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 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 + 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: + 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 + count = 0 + current = self.head + + while current != None: + current = current.next + count +=1 + return count # 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 < 0: + return None + else: + current = self.head + count = 0 + while current: + if count == index: + return current.value + current = current.next + count += 1 + return + + # 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 + else: + 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 + if not self.head : + self.add_first(value) + else: + + node = Node(value) + current = self.head + while current.next: + current = current.next + current.next = node + # method to return the max value in the linked list # returns the data value and not the node def find_max(self): - pass + max = 0 + if self.head == None: + return None + + current = self.head + while current: + if current.value > max: + 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) + # Space Complexity: O(1) def delete(self, value): - pass + current = self.head + previous = None + if not current: + return None + if current.value == value: + self.head = current.next + return + while current: + if current.value == value: + previous.next = current.next + return + previous = current + current = current.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 @@ -86,17 +154,33 @@ 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: + return None + else: + current =self.head + previous = None + next = None + while current: + 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 + before = self.head + after = self.head + while after and after.next: + after = after.next.next + before = before.next + return before.value # find the nth node from the end and return its value # assume indexing starts at 0 while counting to n