diff --git a/linked_list.rb b/linked_list.rb index bcf81853..784b98e4 100644 --- a/linked_list.rb +++ b/linked_list.rb @@ -6,7 +6,7 @@ class Node def initialize(value) @data = value - @next = next + @next = nil end end @@ -19,79 +19,264 @@ 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 def insert(value) - puts "Not implemented" + new_node = Node.new(value) + + if @head != nil # if linked list is not empty + new_node.next = @head + end + + @head = new_node end + # method to find if the linked list contains a node with specified value # returns true if found, false otherwise def search(value) - puts "Not implemented" + current = @head + + while current !=nil + if current.data == value + return true + end + + current = current.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 - puts "Not implemented" + if @head == nil + puts "Error: The linked list is empty. Cannot compute max." + return nil + end + + current = @head + max = current.data + + while current != nil + if current.data > max + max = current.data + end + current = current.next + end + return max end # method to return the min value in the linked list # returns the data value and not the node def find_min - puts "Not implemented" + if @head == nil + puts "Error: The linked list is empty. Cannot compute min." + return nil + end + + current = @head + min = current.data + + while current != nil + if current.data < min + min = current.data + end + current = current.next + end + return min end # method that returns the length of the singly linked list def length - puts "Not implemented" + length = 0 + current = @head + + while current != nil + length +=1 + current = current.next + end + return length end # method to return the value of the nth element from the beginning # assume indexing starts at 0 while counting to n def find_nth_from_beginning(n) - puts "Not implemented" + index = 0 + current = @head + + while current != nil + if index == n + return current.data + end + current = current.next + index += 1 + end + puts "Error: Linked list has fewer than n elements." + return nil end # method to insert a new node with specific data value, assuming the linked # list is sorted in ascending order def insert_ascending(value) - puts "Not implemented" + new_node = Node.new(value) + + if @head == nil + @head = new_node + return + end + + if @head.data > value + new_node.next = @head + @head = new_node + return + end + + current = @head + + while current.next != nil + if current.next.data > value + new_node.next = current.next + current.next = new_node + return + end + current = current.next + end + + current.next = new_node + new_node.next = nil + end + # method to print all the values in the linked list def visit - puts "Not implemented" + if @head == nil + puts "Error: Linked list is empty. No values to print." + return nil + end + current = @head + while current != nil + puts "#{current.data}" + current = current.next + end end # method to delete the first node found with specified value def delete(value) - puts "Not implemented" + if @head == nil + return + end + + if @head.data == value + @head = @head.next + return + end + + current = @head + while current.next != nil + if current.next.data == value + current.next = current.next.next + return + end + current = current.next + end end + # method to reverse the singly linked list # note: the nodes should be moved and not just the values in the nodes def reverse - puts "Not implemented" + + current = @head + previous = nil + + while current !=nil + temp = current.next + current.next = previous + previous = current + current = temp + end + + @head = previous end ## Advanced Exercises # returns the value at the middle element in the singly linked list def find_middle_value - puts "Not implemented" + if @head == nil + return nil + end + + slow = @head + fast = @head.next + + while fast !=nil + fast = fast.next + slow = slow.next + if fast!= nil + fast = fast.next + end + end + return slow.data end # find the nth node from the end and return its value # assume indexing starts at 0 while counting to n def find_nth_from_end(n) - puts "Not implemented" + + current = @head + + count = 0 + while ((current !=nil) && (count != n)) + count +=1 + current = current.next + end + + if current == nil + puts "Fewer than n items in Linked List" + return + end + + behind = @head + ahead = current + while ahead.next !=nil + ahead = ahead.next + behind = behind.next + end + + return behind.data + end + + + # 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. def has_cycle - puts "Not implemented" + + if @head == nil || @head.next == nil + return false + end + + slow = @head + fast = @head + + while fast !=nil + fast = fast.next + slow = slow.next + + if fast!= nil + fast = fast.next + end + if fast == slow + return true + end + end + return false end + # Creates a cycle in the linked list for testing purposes # Assumes the linked list has at least one node def create_cycle @@ -178,6 +363,11 @@ def create_cycle my_linked_list_length = my_linked_list.length puts "BUG: Length should be 4 and not #{my_linked_list_length}" if my_linked_list_length != 4 + + + + + # delete value puts "Deleting node with value 1 from the linked list." my_linked_list.delete(1)