From 888b936b5ce1084f43633d2fb3a1421ebeeaf3cd Mon Sep 17 00:00:00 2001
From: daniela sanchez <dnsanche@gmail.com>
Date: Sun, 16 Feb 2020 22:14:29 -0800
Subject: [PATCH 1/4] Some exercises

---
 lib/linked_list.rb | 114 ++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 102 insertions(+), 12 deletions(-)

diff --git a/lib/linked_list.rb b/lib/linked_list.rb
index 8dee5e8d..8eab8632 100644
--- a/lib/linked_list.rb
+++ b/lib/linked_list.rb
@@ -19,54 +19,129 @@ 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
+      new_node = Node.new(value, @head)
+      @head = new_node 
     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
+      return false if @head == nil
+      
+      current = @head
+      found = false
+      until current == nil
+        if current.data == value
+          found = true
+          break
+        end 
+
+        current = current.next
+      end
+      return found
     end
 
     # method to return the max value in the linked list
     # returns the data value and not the node
     def find_max
-      raise NotImplementedError
+      return nil if @head == nil
+      
+      current = @head
+      max = 0
+      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
+      return nil if @head == nil
+      
+      current = @head
+      min = 0
+      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
+      return 0 if @head == nil
+      
+      current = @head
+      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
+      length = 0
+      current = @head
+      value_to_find = nil
+
+      until current == nil
+        if index == length
+          value_to_find = current.data
+          current = nil
+        end
+        length += 1
+        current == current.next
+      end
+
+      return value_to_find 
     end
 
     # method to print all the values in the linked list
     def visit
-      raise NotImplementedError
+      return nil if @head == nil
+      current = @head
+
+      until current == nil 
+        print current.data
+        current = current.next
+      end 
     end
 
     # method to delete the first node found with specified value
     def delete(value)
-      raise NotImplementedError
+      return nil if @head == nil
+      current = @head
+      previous = current 
+
+      until current == nil || previous.next == nil
+        if current.data == value
+          previous.next == current.next
+          current.next = nil
+        end 
+      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
-      raise NotImplementedError
+      previous = nil
+      current = @head
+
+      until current == nil
+        current = current.next
+        current.next = previous
+
     end
 
 
@@ -94,12 +169,27 @@ def has_cycle
     # returns the value in the first node
     # returns nil if the list is empty
     def get_first
-      raise NotImplementedError
+      if @head == nil
+        return @head
+      else
+        return @head.data
+      end
     end
 
     # method that inserts a given value as a new last node in the linked list
     def add_last(value)
-      raise NotImplementedError
+      if @head == nil
+        add_first(value)
+      else
+        current = @head
+        previous = current
+        new_last_node = Node.new(value, nil)
+
+        until @current.next == nil
+          current = current.next
+        end
+        current.next == new_last_node
+      end
     end
 
     # method that returns the value of the last node in the linked list
@@ -123,7 +213,7 @@ def create_cycle
       # navigate to last node
       current = @head
       while current.next != nil
-          current = current.next
+        current = current.next
       end
 
       current.next = @head # make the last node link to first node

From af24c7a61281dcf9ba32c0698dda11a16012a691 Mon Sep 17 00:00:00 2001
From: daniela sanchez <dnsanche@gmail.com>
Date: Mon, 17 Feb 2020 22:53:51 -0800
Subject: [PATCH 2/4] Only delete and nth from end are missing

---
 lib/linked_list.rb | 69 ++++++++++++++++++++++++++++++++--------------
 1 file changed, 49 insertions(+), 20 deletions(-)

diff --git a/lib/linked_list.rb b/lib/linked_list.rb
index 8eab8632..71ce311e 100644
--- a/lib/linked_list.rb
+++ b/lib/linked_list.rb
@@ -47,7 +47,8 @@ def find_max
       return nil if @head == nil
       
       current = @head
-      max = 0
+      max = current.data
+      
       until current == nil
         if current.data > max
           max = current.data
@@ -91,20 +92,19 @@ def length
     # 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)
-      length = 0
       current = @head
-      value_to_find = nil
 
-      until current == nil
-        if index == length
-          value_to_find = current.data
-          current = nil
+      index.times do 
+        if current != nil
+          current = current.next
         end
-        length += 1
-        current == current.next
       end
 
-      return value_to_find 
+      if current != nil
+        return  current.data
+      else
+        return nil
+      end
     end
 
     # method to print all the values in the linked list
@@ -125,8 +125,9 @@ def delete(value)
       previous = current 
 
       until current == nil || previous.next == nil
+
         if current.data == value
-          previous.next == current.next
+          previous.next == nil
           current.next = nil
         end 
       end
@@ -135,13 +136,20 @@ def delete(value)
     # method to reverse the singly linked list
     # note: the nodes should be moved and not just the values in the nodes
     def reverse
-      previous = nil
+      return if @head.nil?
+      
       current = @head
+      previous = nil
 
-      until current == nil
-        current = current.next
+      until current.next.nil?
+        temp = current.next
         current.next = previous
+        previous = current
+        current = temp
+      end
 
+      current.next = previous
+      @head = current
     end
 
 
@@ -153,9 +161,22 @@ def find_middle_value
 
     # 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
-    end
+    # def find_nth_from_end(n)
+    #   return nil if @head == nil
+
+    #   current = @head
+    #   nth_previous = current
+
+    #   until current.next == nil
+    #     (n - 1).times do
+    #       nth_previous = nth_previous.next
+    #     end
+
+    #     n.times do
+    #       current = current.next
+    #     end
+    #   end
+    # 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.
@@ -185,17 +206,25 @@ def add_last(value)
         previous = current
         new_last_node = Node.new(value, nil)
 
-        until @current.next == nil
+        until current.next == nil
           current = current.next
         end
-        current.next == new_last_node
+        current.next = new_last_node
       end
     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
+      return nil if @head == nil
+
+      current = @head
+
+      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

From ba9689f96a8ccfbee3952680bf60bd1e8132a94c Mon Sep 17 00:00:00 2001
From: daniela sanchez <dnsanche@gmail.com>
Date: Tue, 18 Feb 2020 23:26:12 -0800
Subject: [PATCH 3/4] Delete method missing to pass tests

---
 lib/linked_list.rb | 61 ++++++++++++++++++++--------------------------
 1 file changed, 27 insertions(+), 34 deletions(-)

diff --git a/lib/linked_list.rb b/lib/linked_list.rb
index 71ce311e..b20ad57a 100644
--- a/lib/linked_list.rb
+++ b/lib/linked_list.rb
@@ -121,35 +121,23 @@ def visit
     # method to delete the first node found with specified value
     def delete(value)
       return nil if @head == nil
-      current = @head
-      previous = current 
-
-      until current == nil || previous.next == nil
-
-        if current.data == value
-          previous.next == nil
-          current.next = nil
-        end 
-      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
-      return if @head.nil?
-      
+      return nil if @head == nil
       current = @head
       previous = nil
-
-      until current.next.nil?
-        temp = current.next
+    
+      while current != nil
+        next_value = current.next  
         current.next = previous
         previous = current
-        current = temp
+        current = next_value 
       end
 
-      current.next = previous
-      @head = current
+      @head = previous
     end
 
 
@@ -161,22 +149,27 @@ def find_middle_value
 
     # 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)
-    #   return nil if @head == nil
-
-    #   current = @head
-    #   nth_previous = current
-
-    #   until current.next == nil
-    #     (n - 1).times do
-    #       nth_previous = nth_previous.next
-    #     end
-
-    #     n.times do
-    #       current = current.next
-    #     end
-    #   end
-    # end
+    def find_nth_from_end(n)
+      return nil if @head == nil
+      
+      answer_pointer = @head
+      scanning_pointer = answer_pointer
+ 
+      n.times do 
+        if scanning_pointer.next != nil 
+          scanning_pointer = scanning_pointer.next
+        else
+          return nil
+        end
+      end
+
+      until scanning_pointer.next == nil
+        answer_pointer = answer_pointer.next
+        scanning_pointer = scanning_pointer.next
+      end
+      
+      return answer_pointer.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.

From d3d225e2007840dbe65d2de0f82e423a4f101754 Mon Sep 17 00:00:00 2001
From: daniela sanchez <dnsanche@gmail.com>
Date: Tue, 16 Jun 2020 18:23:42 -0700
Subject: [PATCH 4/4] delete method

---
 lib/linked_list.rb       | 20 ++++++++++++++++++--
 test/linked_list_test.rb |  4 ++--
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/lib/linked_list.rb b/lib/linked_list.rb
index b20ad57a..7838be56 100644
--- a/lib/linked_list.rb
+++ b/lib/linked_list.rb
@@ -64,8 +64,8 @@ def find_min
       return nil if @head == nil
       
       current = @head
-      min = 0
-      until current == nil
+      min = @head.data
+      while current != nil
         if current.data < min
           min = current.data
         end
@@ -121,6 +121,22 @@ def visit
     # method to delete the first node found with specified value
     def delete(value)
       return nil if @head == nil
+
+      if @head.data == value
+        @head = @head.next
+      end
+
+      curr = @head
+      prev = nil
+
+      while curr != nil
+        if curr.data == value
+            prev.next = curr.next
+        end
+        prev = curr
+        curr = curr.next
+      end
+      return @head
     end
 
     # method to reverse the singly linked list
diff --git a/test/linked_list_test.rb b/test/linked_list_test.rb
index d169c9a0..7d9173f9 100644
--- a/test/linked_list_test.rb
+++ b/test/linked_list_test.rb
@@ -174,7 +174,7 @@
             expect(@list.find_max).must_equal 10
             expect(@list.find_min).must_equal 3
 
-            # delete last node
+            # # delete last node
             @list.delete(10)
             expect(@list.get_first).must_equal 3
             expect(@list.length).must_equal 3
@@ -182,7 +182,7 @@
             expect(@list.find_max).must_equal 9
             expect(@list.find_min).must_equal 3
 
-            # delete fist node (requires updating head)
+            # # delete fist node (requires updating head)
             @list.delete(4)
             expect(@list.get_first).must_equal 3
             expect(@list.length).must_equal 2