diff --git a/lib/linked_list.rb b/lib/linked_list.rb index 5e173ebc..72720932 100644 --- a/lib/linked_list.rb +++ b/lib/linked_list.rb @@ -18,87 +18,180 @@ def initialize # 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(value) - raise NotImplementedError + @head = Node.new(value, @head) end # 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(value) - raise NotImplementedError + current_node = @head + + until current_node.nil? + return true if current_node.data == value + current_node = current_node.next + end + + return false end # method to return the max value in the linked list # returns the data value and not the node def find_max - raise NotImplementedError + return nil if @head.nil? + + current_node = @head + max = 0 + until current_node.nil? + if current_node.data > max + max = current_node.data + end + current_node = current_node.next + end + + return max end # method to return the min value in the linked list # returns the data value and not the node - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(n) + # Space Complexity: O(1) def find_min - raise NotImplementedError + return nil if @head.nil? + + current_node = @head + min = current_node.data + + until current_node.nil? + if current_node.data < min + min = current_node.data + end + current_node = current_node.next + end + + return min end # Additional Exercises # returns the value in the first node # returns nil if the list is empty - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(1) + # Space Complexity: O(1) def get_first - raise NotImplementedError + return nil if @head.nil? # I don't understand why this is not passing the test + + return @head.data end # 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(value) - raise NotImplementedError + new_node = Node.new(value) + + current_node = @head + if current_node.nil? + return @head = new_node + end + + until current_node.next.nil? + current_node = current_node.next + end + + current_node.next = new_node end # method that returns the length of the singly linked list - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(1) + # Space Complexity: O(1) def length - raise NotImplementedError + current_node = @head + counter = 0 + until current_node.nil? + counter += 1 + current_node = current_node.next + end + + return counter end # method that returns the value at a given index in the linked list # index count starts at 0 # returns nil 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(index) - raise NotImplementedError + length = self.length + + return nil if index > length + + current_node = @head + + index.times do + current_node = current_node.next + end + + return current_node.data end # method to print all the values in the linked list - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(n) + # Space Complexity: O(1) def visit - raise NotImplementedError + current_node = @head + + return nil if current_node.nil? + until current_node.nil? + puts current_node.data + current_node = current_node.next + end end # method to delete the first node found with specified value - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(n) + # Space Complexity: O(1) def delete(value) - raise NotImplementedError + return nil if @head.nil? + current_node = @head + previous = nil + + until current_node.nil? + if current_node.data == value + # previous.next = current.next + if previous == nil + @head = current_node.next + else + previous.next = current_node.next + end + end + previous = current_node + current_node = current_node.next + end end # 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 - raise NotImplementedError + return nil if @head.nil? + current_node = @head + previous = nil + + until current_node.next.nil? + temp = current_node.next + current_node.next = previous + previous = current_node + current_node = temp + end + + current_node.next = previous + @head = current_node end # method that returns the value of the last node in the linked list @@ -106,7 +199,14 @@ def reverse # Time Complexity: ? # Space Complexity: ? def get_last - raise NotImplementedError + return nil if @head.nil? + + current_node = @head + until current_node.next == nil + current_node = current_node.next + end + + return current_node.data end ## Advanced Exercises @@ -122,7 +222,22 @@ def find_middle_value # Time Complexity: ? # Space Complexity: ? def find_nth_from_end(n) - raise NotImplementedError + return nil if @head.nil? + + current_node = @head + n_ahead = @head + + n.times do + return if n_ahead.next.nil? + n_ahead = n_ahead.next + end + + until n_ahead.next.nil? + current_node = current_node.next + n_ahead = n_ahead.next + end + + return current_node.data end # checks if the linked list has a cycle. A cycle exists if any node in the @@ -131,7 +246,18 @@ def find_nth_from_end(n) # Time Complexity: ? # Space Complexity: ? def has_cycle - raise NotImplementedError + return nil if @head.nil? + + fast = @head + slow = @head + + until fast.nil? || fast.next.nil? + fast = fast.next.next + slow = slow.next + return true if fast == slow + end + + return false end # method to insert a new node with specific data value, assuming the linked @@ -139,7 +265,21 @@ def has_cycle # Time Complexity: ? # Space Complexity: ? def insert_ascending(value) - raise NotImplementedError + return nil if @head.nil? + + current_node = @head + + until current_node.nil? + if value > current_node.data && value <= current_node.next.data + new_node = Node.new(value, current_node.next) + current_node.next = new_node + return + else + current_node = current_node.next + end + end + + return current_node = Node.new(value) end # Helper method for tests