diff --git a/linked_list/linked_list.py b/linked_list/linked_list.py index 63993214..3ef3a074 100644 --- a/linked_list/linked_list.py +++ b/linked_list/linked_list.py @@ -13,67 +13,126 @@ 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 == 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_head = Node(value, self.head) + self.head = new_head # 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 + cur = self.head + while cur != None: + if cur.value == value: + return True + cur = cur.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 + cur = self.head + i = 0 + while cur != None: + cur = cur.next + i += 1 + return i # 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 + cur = self.head + for i in range(index): + if cur == None: + return None + cur = cur.next + return cur.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 self.head == None: + return None + cur = self.head + prev = None + while cur != None: + prev = cur + cur = cur.next + return prev.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 self.head == None: + self.head = Node(value, None) + return + cur = self.head + prev = None + while cur != None: + prev = cur + cur = cur.next + prev.next = Node(value, None) + # 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 + cur = self.head + cur_max = cur.value + cur = cur.next + while cur != None: + if cur.value > cur_max: + cur_max = cur.value + cur = cur.next + return cur_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 + if self.head == None: + return None + if self.head.value == value: + self.head = self.head.next + + prev = self.head + cur = self.head.next + while cur != None and cur.value != value: + prev = cur + cur = cur.next + + if cur != None: + prev.next = cur.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 @@ -86,10 +145,15 @@ 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(n) def reverse(self): - pass + cur = self.head + last_made = None + while cur != None: + last_made = Node(cur.value, last_made) + cur = cur.next + self.head = last_made ## Advanced/ Exercises # returns the value at the middle element in the singly linked list