From a317a96ee8bdd52defe3d73b8f746ddab753a0f3 Mon Sep 17 00:00:00 2001
From: Mariya Burrows <mariya.burrows@gmail.com>
Date: Mon, 17 Feb 2020 21:52:09 -0800
Subject: [PATCH] finished the linked list hw

---
 lib/linked_list.rb       | 173 +++++++++++++++++++++++++++++++++++----
 test/linked_list_test.rb |  84 +++++++++----------
 2 files changed, 200 insertions(+), 57 deletions(-)

diff --git a/lib/linked_list.rb b/lib/linked_list.rb
index 8dee5e8d..6cb0f5ad 100644
--- a/lib/linked_list.rb
+++ b/lib/linked_list.rb
@@ -19,67 +19,190 @@ 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
+      return nil if current.nil?
+      max = current.data
+
+      until 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
     def find_min
-      raise NotImplementedError
+      current = @head
+      return nil if current.nil?
+      min = current.data
+
+      until 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
     def length
-      raise NotImplementedError
+      current = @head
+      return 0 if current.nil?
+      length = 0
+
+      until current.nil?
+        length += 1
+        current = current.next 
+      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 
+      length = 0
+      
+      until current.nil? 
+        length += 1
+        current = current.next
+      end
+
+      return nil if length < index 
+
+      current = @head 
+      index_value = current.data
+
+      (index + 1).times do 
+        index_value = current.data
+        current = current.next
+      end
+  
+      return index_value
     end
 
     # method to print all the values in the linked list
     def visit
-      raise NotImplementedError
+      current = @head
+      return nil if head.nil?
+      
+      until current.nil?
+        p current.data
+      end
+
     end
 
     # method to delete the first node found with specified value
     def delete(value)
-      raise NotImplementedError
+      return nil if @head.nil?
+      current = @head
+      
+      if current.data == value 
+        return @head = current.next 
+      end
+      
+      previous = nil
+      continuing_node = nil
+      
+      until current.next.nil? || current.next.data == value 
+        current = current.next
+      end
+
+      return nil if current.next.nil? 
+      previous = current 
+      continuing_node = previous.next.next
+      previous.next = continuing_node
+      
     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
+      previous = nil 
+      current = @head 
+      return nil if current.nil? 
+      next_node = current.next
+      current.next = nil
+      
+
+      until next_node.nil?
+        previous = current
+        current = next_node
+        next_node = current.next 
+        current.next = previous
+      end
+
+      @head = current
+     
     end
 
 
     ## Advanced Exercises
     # returns the value at the middle element in the singly linked list
     def find_middle_value
-      raise NotImplementedError
+      current = @head
+      temp = current
+      length = 0
+
+      until current.nil?
+        length += 1
+        temp = temp.next
+      end
+
+      middle_node = nil
+      (length / 2).times do 
+        middle_node = current.data
+        current = current.next
+      end
+
+      return middle_node
     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
+      nth_node = nil 
+      current = @head
+      temp = @head 
+      length = 0
+
+      until temp.nil?
+        length += 1
+        temp = temp.next
+      end
+
+      (length - n).times do 
+        nth_node = current.data 
+        current = current.next
+      end
+
+      return nth_node
     end
 
     # checks if the linked list has a cycle. A cycle exists if any node in the
@@ -94,24 +217,44 @@ 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 current.data
     end
 
     # method that inserts a given value as a new last node in the linked list
     def add_last(value)
-      raise NotImplementedError
+      if !@head 
+        @head = Node.new(value)
+        return @head
+      else
+        current = @head
+      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
     end
 
     # Helper method for tests
diff --git a/test/linked_list_test.rb b/test/linked_list_test.rb
index d169c9a0..f8c5c49b 100644
--- a/test/linked_list_test.rb
+++ b/test/linked_list_test.rb
@@ -12,73 +12,73 @@
     before do
         @list = LinkedList.new
     end
-
+    
     describe 'initialize' do
         it 'can be created' do
-
+            
             # Assert
             expect(@list).must_be_kind_of LinkedList
         end
     end
-
+    
     describe 'add_first & get_first' do
         it 'can add values to an empty list' do
             # Act
             @list.add_first(3)
-
+            
             # Assert
             expect(@list.get_first).must_equal 3
         end
-
+        
         it 'will put the last added item to the front of the list' do
             # Act
             @list.add_first(1)
             @list.add_first(2)
-
+            
             # Assert
             expect(@list.get_first).must_equal 2
-
+            
             # Act again
             @list.add_first(3)
-
+            
             # Assert
             expect(@list.get_first).must_equal 3
         end
-
+        
         it 'will return `nil` for `getFirst` if the list is empty' do
-
+            
             expect(@list.get_first).must_be_nil
         end
     end
-
+    
     describe "search" do
         it "can find an element" do
             @list = LinkedList.new
             @list.add_first(3)
             @list.add_first(2)
-
+            
             expect(@list.search(3)).must_equal true
-
+            
             expect(@list.search(2)).must_equal true
         end
-
+        
         it "returns false if the element is not in the list" do
-          @list = LinkedList.new
-          @list.add_first(3)
-          @list.add_first(2)
-          expect(@list.search("pasta")).must_equal false
+            @list = LinkedList.new
+            @list.add_first(3)
+            @list.add_first(2)
+            expect(@list.search("pasta")).must_equal false
         end
-
+        
         it "returns false for an empty list" do
-          expect(@list.search(3)).must_equal false
+            expect(@list.search(3)).must_equal false
         end
     end
-
+    
     describe "length" do
         it "will return 0 for an empty list" do
             expect(@list.length).must_equal 0
         end
-
+        
         it "will return the length for nonempty lists" do
             count = 0
             while count < 5
@@ -88,54 +88,54 @@
             end
         end
     end
-
+    
     describe "addLast & getLast" do
         it "will add to the front if the list is empty" do
             @list.add_last(1)
             expect(@list.get_first).must_equal 1
         end
-
+        
         it "will put new items to the rear of the list" do
             @list.add_last(2)
             expect(@list.length).must_equal 1
             expect(@list.get_last).must_equal 2
-
+            
             @list.add_last(3)
             expect(@list.get_first).must_equal 2
             expect(@list.get_last).must_equal 3
             expect(@list.length).must_equal 2
-
+            
             @list.add_last(4)
             expect(@list.get_first).must_equal 2
             expect(@list.get_last).must_equal 4
             expect(@list.length).must_equal 3
         end
     end
-
+    
     describe 'get_at_index' do
         it 'returns nil if the index is outside the bounds of the list' do
             expect(@list.get_at_index(3)).must_be_nil
         end
-
+        
         it 'can retrieve an item at an index in the list' do
             @list.add_first(1)
             @list.add_first(2)
             @list.add_first(3)
             @list.add_first(4)
-
+            
             expect(@list.get_at_index(0)).must_equal 4
             expect(@list.get_at_index(1)).must_equal 3
             expect(@list.get_at_index(2)).must_equal 2
             expect(@list.get_at_index(3)).must_equal 1
         end
     end
-
+    
     describe 'max and min values' do
         it 'returns nil if the list is empty' do
             expect(@list.find_max()).must_be_nil
             expect(@list.find_min()).must_be_nil
         end
-
+        
         it 'can retrieve the max and min values in the list' do
             count = 0
             while count < 5
@@ -144,28 +144,28 @@
                 expect(@list.find_min).must_equal 0
                 count += 1
             end
-
+            
             @list.add_last(100)
             @list.add_first(-12)
             expect(@list.find_max).must_equal 100
             expect(@list.find_min).must_equal(-12)
         end
     end
-
+    
     describe "delete" do
         it "delete from empty linked list is a no-op" do
             expect(@list.length).must_equal 0
             @list.delete(4)
             expect(@list.length).must_equal 0
         end
-
+        
         it "can delete valid values from list" do
             @list.add_last(9)
             @list.add_last(10)
             @list.add_first(4)
             @list.add_first(3)
             @list.add_first(2)
-
+            
             # delete fist node (requires updating head)
             @list.delete(2)
             expect(@list.get_first).must_equal 3
@@ -173,7 +173,7 @@
             expect(@list.get_last).must_equal 10
             expect(@list.find_max).must_equal 10
             expect(@list.find_min).must_equal 3
-
+            
             # delete last node
             @list.delete(10)
             expect(@list.get_first).must_equal 3
@@ -181,7 +181,7 @@
             expect(@list.get_last).must_equal 9
             expect(@list.find_max).must_equal 9
             expect(@list.find_min).must_equal 3
-
+            
             # delete fist node (requires updating head)
             @list.delete(4)
             expect(@list.get_first).must_equal 3
@@ -191,18 +191,18 @@
             expect(@list.find_min).must_equal 3
         end
     end
-
+    
     describe "nth_from_the_end" do
         it 'returns nil if n is outside the bounds of the list' do
             expect(@list.find_nth_from_end(3)).must_be_nil
         end
-
+        
         it 'can retrieve an item at index n from the end in the list' do
             @list.add_first(1)
             @list.add_first(2)
             @list.add_first(3)
             @list.add_first(4)
-
+            
             expect(@list.find_nth_from_end(0)).must_equal 1
             expect(@list.find_nth_from_end(1)).must_equal 2
             expect(@list.find_nth_from_end(2)).must_equal 3
@@ -210,7 +210,7 @@
             expect(@list.find_nth_from_end(4)).must_be_nil
         end
     end
-
+    
     describe "reverse" do
         it 'can retrieve an item at index n from the end in the list' do
             @list.add_first(4)
@@ -218,7 +218,7 @@
             @list.add_first(2)
             @list.add_first(1)
             @list.reverse
-
+            
             expect(@list.find_nth_from_end(0)).must_equal 1
             expect(@list.find_nth_from_end(1)).must_equal 2
             expect(@list.find_nth_from_end(2)).must_equal 3