From c840a4c39ad8dc8becc01185dc933deb4667c0e1 Mon Sep 17 00:00:00 2001
From: Grace Shea <grace.m.shea@gmail.com>
Date: Sun, 29 Sep 2019 16:27:06 -0700
Subject: [PATCH] completed problems up to adv. exercises

---
 lib/linked_list.rb | 321 ++++++++++++++++++++++++++++-----------------
 1 file changed, 203 insertions(+), 118 deletions(-)

diff --git a/lib/linked_list.rb b/lib/linked_list.rb
index 501c60fb..e11befc1 100644
--- a/lib/linked_list.rb
+++ b/lib/linked_list.rb
@@ -1,4 +1,3 @@
-
 # Defines a node in the singly linked list
 class Node
   attr_reader :data # allow external entities to read value but not write
@@ -12,152 +11,238 @@ 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
+  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: O(1), no need to traverse
+  # Space Complexity: O(1)
+  def add_first(value)
+    node = Node.new(value, @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: O(n), we may need to traverse all nodes
+  # Space Complexity: O(1)
+  def search(value)
+    current = @head
+    until !current
+      if current.data == value
+        return true
+      end
+      current = current.next
     end
+    return false
+  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
+  # method to return the max value in the linked list
+  # returns the data value and not the node
+  # Time Complexity: O(n), we may need to traverse all nodes
+  # Space Complexity O(1)
+  def find_max
+    temp_node = @head
+    if temp_node == nil
+      return nil
+    end
+    temp_max = temp_node.data
+    until temp_node == nil
+      if temp_node.data > temp_max
+        temp_max = temp_node.data
+      end
+      temp_node = temp_node.next
     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
+    return temp_max
+  end
+
+  # method to return the min value in the linked list
+  # returns the data value and not the node
+  # Time Complexity: O(n), we may need to traverse all nodes
+  # Space Complexity: O(1)
+  def find_min
+    temp_node = @head
+    if temp_node == nil
+      return nil
     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
+    temp_min = temp_node.data
+    until temp_node == nil
+      if temp_node.data < temp_min
+        temp_min = temp_node.data
+      end
+      temp_node = temp_node.next
     end
+    return temp_min
+  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 that returns the length of the singly linked list
+  # Time Complexity: O(n), we may need to traverse all nodes
+  # Space Complexity: O(1)
+  def length
+    counter = 0
+    temp = @head
+    if @head == nil
+      return counter
+    else
+      until (temp == nil)
+        temp = temp.next
+        counter += 1
+      end
     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: O(n), we may need to traverse all nodes
+  # Space Complexity: O(1)
+  def get_at_index(index)
+    temp_node = @head
+    counter = 0
+
+    until counter == index
+      if temp_node == nil && counter < index
+        return nil
+      end
 
-    # method that returns the length of the singly linked list
-    # Time Complexity:  
-    # Space Complexity
-    def length
-      raise NotImplementedError
+      temp_node = temp_node.next
+      counter += 1
     end
+    return temp_node.data
+  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 to print all the values in the linked list
+  # Time Complexity: O(n), we may need to traverse all nodes
+  # Space Complexity: O(1)
+  def visit
+    current = @head
+    if !current
+      puts "There are no values to print"
+    else
+      until !current
+        puts current.value
+        current = current.next
+      end
     end
+  end
 
-    # 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), we may need to traverse all nodes
+  # Space Complexity O(1)
+  def delete(value)
+    temp_node = @head
+    return if temp_node == nil
 
-    # method to delete the first node found with specified value
-    # Time Complexity:  
-    # Space Complexity
-    def delete(value)
-      raise NotImplementedError
+    if temp_node.data == value
+      @head = temp_node.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
+    until temp_node.next == nil
+      temp_next = temp_node.next
+      if temp_next.data == value
+        temp_node.next = temp_next.next
+        return
+      end
+      temp_node = temp_next
     end
+    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: O(n), we may need to traverse all nodes
+  # Space Complexity: O(1)
+  def reverse
+    current = @head
+    prev = nil
+
+    while current
+      temp = current.next
+      current.next = prev
+      prev = current
+      current = temp
+    end
+    @head = prev
+    return
+  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)
-      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
 
-    # 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
+  # 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
 
+  # 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
-      raise NotImplementedError
-    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
-    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
+  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
-    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
+  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
+  # 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
+  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
+  # 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
 
-      # 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
-end
+
+    current.next = @head # make the last node link to first node
+  end
+end
\ No newline at end of file