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Danielle Birbal - Linked List #2

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567 changes: 338 additions & 229 deletions linked_list.rb
Original file line number Diff line number Diff line change
@@ -1,229 +1,338 @@

# Defines a node in the singly linked list
class Node
attr_reader :data # allow external entities to read value but not write
attr_accessor :next # allow external entities to read or write next node

def initialize(value)
@data = value
@next = next
end
end

# Defines the singly linked list
class LinkedList
def initialize
@head = nil # keep the head private. Not accessible outside this class
end

# 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"
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"
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"
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"
end

# method that returns the length of the singly linked list
def length
puts "Not implemented"
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"
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"
end

# method to print all the values in the linked list
def visit
puts "Not implemented"
end

# method to delete the first node found with specified value
def delete(value)
puts "Not implemented"
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"
end

## Advanced Exercises
# returns the value at the middle element in the singly linked list
def find_middle_value
puts "Not implemented"
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"
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"
end

# Creates a cycle in the linked list for testing purposes
# Assumes the linked list has at least one node
def create_cycle
return if @head == nil # don't do anything if the linked list is empty

# navigate to last node
current = @head
while current.next != nil
current = current.next
end

current.next = @head # make the last node link to first node
end
end

## --- END of class definitions --- ##

# Create an object of linked list class
my_linked_list = LinkedList.new()

# Add some values to the linked list
puts "Adding 5, 3 and 1 to the linked list."
my_linked_list.insert(5)
my_linked_list.insert(3)
my_linked_list.insert(1)

# print all elements
puts "Printing elements in the linked list:"
my_linked_list.visit

# Find the value at the nth node
puts "Confirming values in the linked list using find_nth_from_beginning method."
value = my_linked_list.find_nth_from_beginning(2)
puts "BUG: Value at index 2 should be 5 and is #{value}" if value != 5
value = my_linked_list.find_nth_from_beginning(1)
puts "BUG: Value at index 1 should be 3 and is #{value}" if value != 3
value = my_linked_list.find_nth_from_beginning(0)
puts "BUG: Value at index 0 should be 1 and is #{value}" if value != 1

# print all elements
puts "Printing elements in the linked list:"
my_linked_list.visit

# Insert ascending
puts "Adding 4 in ascending order."
my_linked_list.insert_ascending(4)
# check newly inserted value
puts "Checking values by calling find_nth_from_beginning method."
value = my_linked_list.find_nth_from_beginning(2)
puts "BUG: Value at index 2 should be 4 and is #{value}" if value != 4
value = my_linked_list.find_nth_from_beginning(3)
puts "BUG: Value at index 3 should be 5 and is #{value}" if value != 5
value = my_linked_list.find_nth_from_beginning(1)
puts "BUG: Value at index 1 should be 3 and is #{value}" if value != 3

# Insert ascending
puts "Adding 6 in ascening order."
my_linked_list.insert_ascending(6)

# print all elements
puts "Printing elements in the linked list:"
my_linked_list.visit

# vaidate length
puts "Confirming length of the linked list."
my_linked_list_length = my_linked_list.length
puts "BUG: Length should be 5 and not #{my_linked_list_length}" if my_linked_list_length != 5

# find min and max
puts "Confirming min and max values in the linked list."
min = my_linked_list.find_min
puts "BUG: Min value should be 1 and not #{min}" if min != 1
max = my_linked_list.find_max
puts "BUG: Max value should be 5 and not #{max}" if max != 6

# delete value
puts "Deleting node with value 5 from the linked list."
my_linked_list.delete(5)
# print all elements
puts "Printing elements in the linked list:"
my_linked_list.visit
# validate length
puts "Confirming length of the linked list."
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)
# print all elements
puts "Printing elements in the linked list:"
my_linked_list.visit
# validate length
puts "Confirming length of the linked list."
my_linked_list_length = my_linked_list.length
puts "BUG: Length should be 3 and not #{my_linked_list_length}" if my_linked_list_length != 3

# find middle element
puts "Confirming middle value in the linked list."
middle = my_linked_list.find_middle_value
puts "BUG: Middle value should be 4 and not #{middle}" if middle != 4

# reverse the linked list
puts "Reversing the linked list."
my_linked_list.reverse
# print all elements
puts "Printing elements in the linked list:"
my_linked_list.visit
# verify the reversed list
puts "Verifying the reveresed linked list by calling find_nth_from_beginning method."
value = my_linked_list.find_nth_from_beginning(2)
puts "BUG: Value at index 2 should be 3 and is #{value}" if value != 3
value = my_linked_list.find_nth_from_beginning(1)
puts "BUG: Value at index 1 should be 4 and is #{value}" if value != 4
value = my_linked_list.find_nth_from_beginning(0)
puts "BUG: Value at index 0 should be 6 and is #{value}" if value != 6

# nth from the end
puts "Verifying find_nth_from_end method."
value = my_linked_list.find_nth_from_end(0)
puts "BUG: Value at index 0 from the end, should be 3 and is #{value}" if value != 3
value = my_linked_list.find_nth_from_end(1)
puts "BUG: Value at index 1 from the end, should be 4 and is #{value}" if value != 4
value = my_linked_list.find_nth_from_end(2)
puts "BUG: Value at index 2 from the end, should be 6 and is #{value}" if value != 6

# check for cycle
puts "Checking the linked list for cycle."
puts "BUG: Should not have a cycle." if my_linked_list.has_cycle

# create cycle and then test for it
puts "Creating a cycle in the linked list."
my_linked_list.create_cycle
puts "Checking the linked list for cycle."
puts "BUG: Should not have a cycle." if !(my_linked_list.has_cycle)

# Defines a node in the singly linked list
class Node
attr_reader :data # allow external entities to read value but not write
attr_accessor :next # allow external entities to read or write next node

def initialize(value)
@data = value
@next = nil
end
end

# Defines the singly linked list
class LinkedList
def initialize
@head = nil # keep the head private. Not accessible outside this class
end

# 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
# Shruti: Just for added practice, I recommend adding time and space complexities as comment before each method
def insert(value)
new_node = Node.new(value)

temp = @head
@head = new_node
new_node.next = temp
end

# method to find if the linked list contains a node with specified value
# returns true if found, false otherwise
def search(value)
node = @head
until node.nil?
return true if node.data == value
node = node.next
end
false
end

# method to return the max value in the linked list
# returns the data value and not the node
def find_max
node = @head
largest_node = @head
until node.nil?
largest_node = node if node.data > largest_node.data
node = node.next
end

largest_node.data # Shruti: check that @head is not nil before doing this.
end

# method to return the min value in the linked list
# returns the data value and not the node
def find_min
node = @head
smallest_node = @head
until node.nil?
smallest_node = node if node.data < smallest_node.data
node = node.next
end

smallest_node.data #Shruti: Confirm that the list is not empty aka the head is not nil.
end

# method that returns the length of the singly linked list
def length
counter = 0
node = @head

until node.nil?
counter += 1
node = node.next
end

counter
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)
node = @head
n.times do
return false if node.next.nil? #Shruti: As a side note, this is good to discuss with the interviewer. Return nil, throw exceptions
node = node.next
end
node.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)
new_node = Node.new(value)
node = @head
node = node.next until node.next.nil? || node.next.data > value
temp = node.next
node.next = new_node
new_node.next = temp
end

# method to print all the values in the linked list
def visit
node = @head.next
print @head.data
until node.nil?
print node.data
node = node.next
end
end

# method to delete the first node found with specified value
def delete(value)
return if @head.nil?

if @head.data == value
@head = @head.next
return
end

current = @head
until current.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
current = @head
previous = nil
temp = current.next

until 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
return if @head.nil?
return @head.data if @head.next.nil?

slow = @head
fast = @head.next

until fast.nil?
slow = slow.next
fast = fast.next
fast = fast.next unless fast.nil?
end

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)
i = 0
current = @head

until i == n
current = current.next
i += 1
end

trailing_current = @head

until current.next.nil?
current = current.next
trailing_current = trailing_current.next
end

trailing_current.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
return false if @head.nil? || @head.next.nil?

slow = @head
fast = @head

until fast.nil?
slow = slow.next
fast = fast.next
fast = fast.next unless fast.nil?
return true if fast == slow
end

false
end

# Creates a cycle in the linked list for testing purposes
# Assumes the linked list has at least one node
def create_cycle
return if @head.nil? # don't do anything if the linked list is empty

# navigate to last node
current = @head
current = current.next until current.next.nil?

current.next = @head # make the last node link to first node
end
end

## --- END of class definitions --- ##

# Create an object of linked list class
my_linked_list = LinkedList.new

# Add some values to the linked list
puts 'Adding 5, 3 and 1 to the linked list.'
my_linked_list.insert(5)
my_linked_list.insert(3)
my_linked_list.insert(1)

# print all elements
puts 'Printing elements in the linked list:'
my_linked_list.visit

# Find the value at the nth node
puts 'Confirming values in the linked list using find_nth_from_beginning method.'
value = my_linked_list.find_nth_from_beginning(2)
puts "BUG: Value at index 2 should be 5 and is #{value}" if value != 5
value = my_linked_list.find_nth_from_beginning(1)
puts "BUG: Value at index 1 should be 3 and is #{value}" if value != 3
value = my_linked_list.find_nth_from_beginning(0)
puts "BUG: Value at index 0 should be 1 and is #{value}" if value != 1

# print all elements
puts 'Printing elements in the linked list:'
my_linked_list.visit

# Insert ascending
puts 'Adding 4 in ascending order.'
my_linked_list.insert_ascending(4)
# check newly inserted value
puts 'Checking values by calling find_nth_from_beginning method.'
value = my_linked_list.find_nth_from_beginning(2)
puts "BUG: Value at index 2 should be 4 and is #{value}" if value != 4
value = my_linked_list.find_nth_from_beginning(3)
puts "BUG: Value at index 3 should be 5 and is #{value}" if value != 5
value = my_linked_list.find_nth_from_beginning(1)
puts "BUG: Value at index 1 should be 3 and is #{value}" if value != 3

# Insert ascending
puts 'Adding 6 in ascening order.'
my_linked_list.insert_ascending(6)

# print all elements
puts 'Printing elements in the linked list:'
my_linked_list.visit

# vaidate length
puts 'Confirming length of the linked list.'
my_linked_list_length = my_linked_list.length
puts "BUG: Length should be 5 and not #{my_linked_list_length}" if my_linked_list_length != 5

# find min and max
puts 'Confirming min and max values in the linked list.'
min = my_linked_list.find_min
puts "BUG: Min value should be 1 and not #{min}" if min != 1
max = my_linked_list.find_max
puts "BUG: Max value should be 5 and not #{max}" if max != 6

# delete value
puts 'Deleting node with value 5 from the linked list.'
my_linked_list.delete(5)
# print all elements
puts 'Printing elements in the linked list:'
my_linked_list.visit
# validate length
puts 'Confirming length of the linked list.'
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)
# print all elements
puts 'Printing elements in the linked list:'
my_linked_list.visit
# validate length
puts 'Confirming length of the linked list.'
my_linked_list_length = my_linked_list.length
puts "BUG: Length should be 3 and not #{my_linked_list_length}" if my_linked_list_length != 3

# find middle element
puts 'Confirming middle value in the linked list.'
middle = my_linked_list.find_middle_value
puts "BUG: Middle value should be 4 and not #{middle}" if middle != 4

# reverse the linked list
puts 'Reversing the linked list.'
my_linked_list.reverse
# print all elements
puts 'Printing elements in the linked list:'
my_linked_list.visit
# verify the reversed list
puts 'Verifying the reveresed linked list by calling find_nth_from_beginning method.'
value = my_linked_list.find_nth_from_beginning(2)
puts "BUG: Value at index 2 should be 3 and is #{value}" if value != 3
value = my_linked_list.find_nth_from_beginning(1)
puts "BUG: Value at index 1 should be 4 and is #{value}" if value != 4
value = my_linked_list.find_nth_from_beginning(0)
puts "BUG: Value at index 0 should be 6 and is #{value}" if value != 6

# nth from the end
puts 'Verifying find_nth_from_end method.'
value = my_linked_list.find_nth_from_end(0)
puts "BUG: Value at index 0 from the end, should be 3 and is #{value}" if value != 3
value = my_linked_list.find_nth_from_end(1)
puts "BUG: Value at index 1 from the end, should be 4 and is #{value}" if value != 4
value = my_linked_list.find_nth_from_end(2)
puts "BUG: Value at index 2 from the end, should be 6 and is #{value}" if value != 6

# check for cycle
puts 'Checking the linked list for cycle.'
puts 'BUG: Should not have a cycle.' if my_linked_list.has_cycle

# create cycle and then test for it
puts 'Creating a cycle in the linked list.'
my_linked_list.create_cycle
puts 'Checking the linked list for cycle.'
puts 'BUG: Should not have a cycle.' unless my_linked_list.has_cycle