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Angela Oh #16

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322 changes: 206 additions & 116 deletions lib/linked_list.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -12,152 +12,242 @@ def initialize(value, next_node = nil)

# Defines the singly linked list
class LinkedList
def initialize
@head = nil # keep the head private. Not accessible outside this class
end
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
# Time Complexity:
# Space Complexity
def add_first(value)
raise NotImplementedError
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
# Time Complexity: O(1)
# Space Complexity: O(1)
def add_first(value)
new_node = Node.new(value)
new_node.next = @head
@head = new_node
return new_node.data
end

# method to find if the linked list contains a node with specified value
# returns true if found, false otherwise
# Time Complexity:
# Space Complexity
def search(value)
raise NotImplementedError
end
# method to find if the linked list contains a node with specified value
# returns true if found, false otherwise
# Time Complexity:
# Space Complexity
def search(value)
raise NotImplementedError
end

# method to return the max value in the linked list
# returns the data value and not the node
# Time Complexity:
# Space Complexity
def find_max
raise NotImplementedError
# method to return the max value in the linked list
# returns the data value and not the node
# Time Complexity: O(n)
# Space Complexity: O(1)
def find_max
return nil if @head.nil?
current = @head
max = current.data

until current.next.nil?
current = current.next
if max < current.data
max = current.data
end
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
def find_min
raise NotImplementedError
# method to return the min value in the linked list
# returns the data value and not the node
# Time Complexity: O(n)
# Space Complexity: O(1)
def find_min
return nil if @head.nil?

return nil if @head.nil?
current = @head
min = current.data

until current.next.nil?
current = current.next
if min > current.data
min = current.data
end
end
return min
end

# method that returns the length of the singly linked list
# Time Complexity: O(n)
# Space Complexity: O(1)
def length
current = @head
return 0 if @head.nil?
return 1 if current.next.nil?

# method that returns the length of the singly linked list
# Time Complexity:
# Space Complexity
def length
raise NotImplementedError
count = 1
until current.next.nil?
current = current.next
count += 1
end
return count
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
def get_at_index(index)
raise NotImplementedError
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: O(n)
# Space Complexity: O(1)
def get_at_index(index)
return nil if index > (self.length - 1)

# method to print all the values in the linked list
# Time Complexity:
# Space Complexity
def visit
raise NotImplementedError
current = @head
until index == 0
current = current.next
index -= 1
end

# method to delete the first node found with specified value
# Time Complexity:
# Space Complexity
def delete(value)
raise NotImplementedError
end
return current.data
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
def reverse
raise NotImplementedError
# method to print all the values in the linked list
# Time Complexity:
# Space Complexity
def visit
raise NotImplementedError
end

# method to delete the first node found with specified value
# Time Complexity: O(n)
# Space Complexity: O(1)
def delete(value)
return 0 if @head.nil?
current = @head
previous = nil

# if deleting from front
if current.data == value
@head = current.next
return
else # if deleting from somewhere in middle or end
until current.data == value
previous = current
current = current.next
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What about if the value is not in the list. You could try to do .data on nil.

end
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
# Time Complexity: O(n)
# Space Complexity: O(1)
def reverse
previous = nil
current = @head

## Advanced Exercises
# returns the value at the middle element in the singly linked list
# Time Complexity:
# Space Complexity
def find_middle_value
raise NotImplementedError
while current != nil
next_node = current.next
current.next = previous
previous = current
current = next_node
end

# find the nth node from the end and return its value
# assume indexing starts at 0 while counting to n
# Time Complexity:
# Space Complexity
def find_nth_from_end(n)
raise NotImplementedError
end
@head = previous
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.
# Time Complexity:
# Space Complexity
def has_cycle
raise NotImplementedError
end
## Advanced Exercises
# returns the value at the middle element in the singly linked list
# Time Complexity:
# Space Complexity
def find_middle_value
raise NotImplementedError
end

# find the nth node from the end and return its value
# assume indexing starts at 0 while counting to n
# Time Complexity:
# Space Complexity
def find_nth_from_end(n)
return nil if n > self.length - 1

# Additional Exercises
# returns the value in the first node
# returns nil if the list is empty
# Time Complexity:
# Space Complexity
def get_first
raise NotImplementedError
end
index = self.length - n - 1

# method that inserts a given value as a new last node in the linked list
# Time Complexity:
# Space Complexity
def add_last(value)
raise NotImplementedError
i = 0
current = @head
while i < index
current = current.next
i += 1
end

# method that returns the value of the last node in the linked list
# returns nil if the linked list is empty
# Time Complexity:
# Space Complexity
def get_last
raise NotImplementedError
return 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.
# Time Complexity:
# Space Complexity
def has_cycle
raise NotImplementedError
end

# Additional Exercises
# returns the value in the first node
# returns nil if the list is empty
# Time Complexity:
# Space Complexity
def get_first
return @head.nil? ? nil : @head.data
end

# method that inserts a given value as a new last node in the linked list
# Time Complexity:
# Space Complexity
def add_last(value)
new_node = Node.new(value)
if self.length == 0
@head = new_node
else
last = @head
until last.next.nil?
last = last.next
end
last.next = new_node
end
end

# method that returns the value of the last node in the linked list
# returns nil if the linked list is empty
# Time Complexity:
# Space Complexity
def get_last
return nil if @head.nil?

# method to insert a new node with specific data value, assuming the linked
# list is sorted in ascending order
# Time Complexity:
# Space Complexity
def insert_ascending(value)
raise NotImplementedError
current = @head
until current.next.nil?
current = current.next
end

# Helper method for tests
# 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
return current.data
end

# navigate to last node
current = @head
while current.next != nil
current = current.next
end
# method to insert a new node with specific data value, assuming the linked
# list is sorted in ascending order
# Time Complexity:
# Space Complexity
def insert_ascending(value)
raise NotImplementedError
end

# Helper method for tests
# 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

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