diff --git a/lib/linked_list.rb b/lib/linked_list.rb index 8dee5e8d..cfcff9af 100644 --- a/lib/linked_list.rb +++ b/lib/linked_list.rb @@ -19,74 +19,170 @@ 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 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 def search(value) - raise NotImplementedError + current = @head + + until current.nil? + return true if current.data == value + 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 - raise NotImplementedError + current = @head + max = current + return nil if current.nil? + + until current.nil? + max = current if current.data > max.data + current = current.next + end + return max.data end # method to return the min value in the linked list # returns the data value and not the node def find_min - raise NotImplementedError + current = @head + min = current + return nil if current.nil? + + until current.nil? + min = current if current.data < min.data + current = current.next + end + return min.data end # method that returns the length of the singly linked list def length - raise NotImplementedError + current = @head + length = 0 + return 0 if current.nil? + + until current.nil? + current = current.next + length += 1 + end + return length 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 def get_at_index(index) - raise NotImplementedError + current = @head + current_index = 0 + + index.times do |i| + return nil if current.nil? + current = current.next + end + + return current.data end # method to print all the values in the linked list def visit - raise NotImplementedError + current = @head + + until current.nil? + print current.data + current = current.next + end end # method to delete the first node found with specified value def delete(value) - raise NotImplementedError + current = @head + previous = nil + + return nil if current.nil? + until current.data == value + previous = current + current = current.next + end + + if previous.nil? + @head = current.next + else + previous.next = 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 - raise NotImplementedError + current = @head + previous = nil + + until current.nil? + temp = current + current = current.next + temp.next = previous + previous = temp + end + @head = previous end ## Advanced Exercises # returns the value at the middle element in the singly linked list def find_middle_value - raise NotImplementedError + current = @head + middle = current + + return nil if current.nil? + until current.nil? + middle.next = middle + current.next.next = current + end + return middle 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) - raise NotImplementedError + current = @head + from_end = current + + return nil if current.nil? + + n.times do + return nil if current.next.nil? + current = current.next + end + + until current.next.nil? + return from_end.data if from_end.next.nil? + from_end = from_end.next + current = current.next + end + return from_end.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 - raise NotImplementedError + slow = @head + fast = @head + + until fast.nil? + slow = slow.next + fast = fast.next.next + return true if slow == fast + end + return false end @@ -94,24 +190,58 @@ def has_cycle # returns the value in the first node # returns nil if the list is empty def get_first - raise NotImplementedError + current = @head + + return nil if current.nil? + return @head.data end # method that inserts a given value as a new last node in the linked list def add_last(value) - raise NotImplementedError + current = @head + + if current.nil? + @head = Node.new(value) + return + end + + until current.next.nil? + current = current.next + end + + current.next = Node.new(value) end # method that returns the value of the last node in the linked list # returns nil if the linked list is empty def get_last - raise NotImplementedError + current = @head + + return nil if current.nil? + until current.next.nil? + current = current.next + end + return current.data end # method to insert a new node with specific data value, assuming the linked # list is sorted in ascending order def insert_ascending(value) - raise NotImplementedError + current = @head + + if current.nil? + @head = Node.new(value) + end + + until current.nil? + if value.data > last.data && value.data < current.data + new_node = Node.new(value, current.next) + current.next = new_node + return + else + current = current.next + end + end end # Helper method for tests @@ -129,3 +259,4 @@ def create_cycle current.next = @head # make the last node link to first node end end + diff --git a/test/linked_list_test.rb b/test/linked_list_test.rb index 22b55ef0..4b84cd0d 100644 --- a/test/linked_list_test.rb +++ b/test/linked_list_test.rb @@ -1,6 +1,5 @@ require 'minitest/autorun' require 'minitest/reporters' -require 'minitest/skip_dsl' require_relative 'test_helper'