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Time - Hannah T #42

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20ff9d0
all test passed
Sep 25, 2020
849a1e8
fixed space and time complexity
Sep 25, 2020
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342 changes: 229 additions & 113 deletions lib/linked_list.rb
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@

require "pry"
# Defines a node in the singly linked list
class Node
attr_reader :data # allow external entities to read value but not write
Expand All @@ -12,150 +12,266 @@ 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)
Comment on lines +19 to +23
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👍

node = Node.new(value)
node.next = @head
@head = node
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
# method to find if the linked list contains a node with specified value
# returns true if found, false otherwise
# Time Complexity: O(n)
# Space Complexity: O(1)
def search(value)
Comment on lines +29 to +33
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👍

current = @head
while 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
# 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(n)
def find_max
Comment on lines +42 to +46
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👍 , however the space complexity is O(1) since you're not building a new list.

return nil if !@head
current = @head
max = -(Float::INFINITY)
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
# 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
Comment on lines +59 to +63
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👍

return nil if !@head
current = @head
min = Float::INFINITY
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
# Time Complexity: ?
# Space Complexity: ?
def length
raise NotImplementedError
# method that returns the length of the singly linked list
# Time Complexity: O(n)
# Space Complexity: O(1)
def length
Comment on lines +76 to +79
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👍

counter = 0
current = @head
while current != nil
counter += 1
current = current.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: ?
def get_at_index(index)
raise NotImplementedError
# 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)
Comment on lines +89 to +94
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👍

i = 0
current = @head
while current != nil
return current.data if index == i
i += 1
current = current.next
end
return nil
end

# method to print all the values in the linked list
# Time Complexity: ?
# Space Complexity: ?
def visit
raise NotImplementedError
# method to print all the values in the linked list
# Time Complexity: O(n)
# Space Complexity: O(1)
def visit
Comment on lines +105 to +108
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👍

current = @head
while current != nil
puts current.data
current = current.next
end
end

# method to delete the first node found with specified value
# Time Complexity: ?
# Space Complexity: ?
def delete(value)
raise NotImplementedError
# method to delete the first node found with specified value
# Time Complexity: O(1)
# Space Complexity: O(1)
def delete(value)
Comment on lines +116 to +119
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👍 , However since this method traverses the list until it finds the given value and then deletes it. So the time complexity is O(n)

return nil if !@head
if @head.data == value
@head = @head.next
return
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
current = @head
while 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
# Time Complexity: O(n)
# Space Complexity: O(1)
def reverse
Comment on lines +135 to +139
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👍 , nicely done.

prev = nil
next_node = nil
current = @head
while current != nil

next_node = current.next
current.next = prev
prev = current
current = next_node
end
@head = prev
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
## Advanced Exercises
# returns the value at the middle element in the singly linked list
# Time Complexity: O(n)
# Space Complexity: O(1)
def find_middle_value
Comment on lines +153 to +157
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👍 , Well done. I like the slow and fast pointers. Well done.

return nil if !@head
slow = @head
fast = @head
while fast.next != nil
slow = slow.next
fast = fast.next.next
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
# Time Complexity: ?
# Space Complexity: ?
def find_nth_from_end(n)
raise NotImplementedError
# find the nth node from the end and return its value
# assume indexing starts at 0 while counting to n
# Time Complexity: O(n)
# Space Complexity: O(1)
def find_nth_from_end(n)
return nil if !@head
current = @head
index = 1
while current != nil
if length - index == n
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Just a note, that length is a method that traverses the list each time. So this makes it O(n^2) time complexity.

Better would be to save the length into a local variable and then use that local variable in the loop.

return current.data
end
index += 1
current = current.next
end
return nil
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
# 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
Comment on lines +186 to +191
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👍 , but what would the time complexity be?

return false if !@head || @head.next = nil
slow = @head
fast = @head
while fast != nil
slow = slow.next
fast = fast.next
if fast != nil
fast = fast.next
end
return true if fast == slow
end
return false
end

# Additional Exercises
# returns the value in the first node
# returns nil if the list is empty
# Time Complexity: O(1)
# Space Complexity: O(1)
def get_first
Comment on lines +206 to +211
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👍

return @head.data if @head
return nil
end

# 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
# method that inserts a given value as a new last node in the linked list
# Time Complexity: O(1)
# Space Complexity: O(1)
def add_last(value)
Comment on lines +216 to +219
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This method works, but since you traverse the list until the end of the list... the time complexity is O(n)

new_node = Node.new(value)
if !@head
@head = new_node
return
end

# 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
current = @head
while current.next != nil
current = current.next
end
current.next = new_node
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
# method that returns the value of the last node in the linked list
# returns nil if the linked list is empty
# Time Complexity: O(1)
# Space Complexity: O(1)
def get_last
Comment on lines +232 to +236
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Similar issues to the above method.

return nil if @head == nil
current = @head
while 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
# Time Complexity: ?
# Space Complexity: ?
def insert_ascending(value)
raise NotImplementedError
# method to insert a new node with specific data value, assuming the linked
# list is sorted in ascending order
# Time Complexity: O(n)
# Space Complexity: O(1)
def insert_ascending(value)
Comment on lines +245 to +249
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👍

new_node = Node.new(value)
if @head == nil
@head = new_node
return
end
current = @head
while current.next && current.next.value <= value
current = current.next
end
new_node.next = current.next
current.next = new_node
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

# navigate to last node
current = @head
while 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

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