diff --git a/.vscode/launch.json b/.vscode/launch.json
index f5d9fc7..93fecc4 100644
--- a/.vscode/launch.json
+++ b/.vscode/launch.json
@@ -51,7 +51,7 @@
             "environment": [],
             "MIMode": "gdb",
             "miDebuggerPath": "/usr/bin/gdb",
-            "preLaunchTask": "C/C++: g++ build active file"
+            "preLaunchTask": "C/C++: g++ build single active file"
         },
         {
             "name": "nybusninesses",
diff --git a/.vscode/tasks.json b/.vscode/tasks.json
index 9a9af73..8aa32e9 100644
--- a/.vscode/tasks.json
+++ b/.vscode/tasks.json
@@ -25,6 +25,32 @@
                 "isDefault": true
             },
             "detail": "Task generated by Debugger."
+        },
+        {
+            "type": "cppbuild",
+            "label": "C/C++: g++ build single active file",
+            "command": "/usr/bin/g++",
+            "args": [
+                "-fdiagnostics-color=always",
+                "-std=c++17",
+                "-Wall",
+                "-Wextra",
+                "-g",
+                "${file}",
+                "-o",
+                "${fileDirname}/${fileBasenameNoExtension}"
+            ],
+            "options": {
+                "cwd": "${fileDirname}"
+            },
+            "problemMatcher": [
+                "$gcc"
+            ],
+            "group": {
+                "kind": "build",
+                "isDefault": true
+            },
+            "detail": "Task generated by Debugger."
         }
     ],
     "version": "2.0.0"
diff --git a/labs/list_implementation/checkpoint1.cpp b/labs/list_implementation/checkpoint1.cpp
index 3e3a35f..4c6c412 100644
--- a/labs/list_implementation/checkpoint1.cpp
+++ b/labs/list_implementation/checkpoint1.cpp
@@ -28,12 +28,8 @@ int main() {
   // clear out the list
   a.clear();
 
-  /*
-  assert (a.size() == 0);
-  */
-  
+  assert (a.size() == 0);  
 
-  /*
   // simple tests of push_front, pop_front, and pop_back
   a.push_front(5);
   a.push_back(7);
@@ -66,7 +62,6 @@ int main() {
   a.pop_front();
   assert (a.size() == 0);
   assert (a.begin() == a.end());
-  */
 
   return 0;
 }
diff --git a/labs/list_implementation/checkpoint2 b/labs/list_implementation/checkpoint2
new file mode 100755
index 0000000..f5eac4d
Binary files /dev/null and b/labs/list_implementation/checkpoint2 differ
diff --git a/labs/list_implementation/checkpoint2.cpp b/labs/list_implementation/checkpoint2.cpp
index e3631d8..d6d1701 100644
--- a/labs/list_implementation/checkpoint2.cpp
+++ b/labs/list_implementation/checkpoint2.cpp
@@ -21,6 +21,36 @@ public:
 	NodeB* prev;
 };
 
+template <typename NodeType>
+void PushBack(NodeType*& head, NodeType* newNode) {
+    // If the list is empty, newNode becomes the head
+    if (!head) {
+        head = newNode;
+    } else {
+        // Otherwise, find the tail and attach there
+        NodeType* current = head;
+        while (current->next != nullptr) {
+            current = current->next;
+        }
+        current->next = newNode;
+        newNode->prev = current;
+    }
+}
+
+template <typename NodeType>
+void PrintList(NodeType* head) {
+    NodeType* current = head;
+    while (current != nullptr) {
+        // For doubles, you might do: std::cout << std::fixed << std::setprecision(5);
+        std::cout << current->data;
+        if (current->next != nullptr) {
+            std::cout << " -> ";
+        }
+        current = current->next;
+    }
+    std::cout << " -> nullptr" << std::endl;
+}
+
 int main() {
 	// Part 1: test NodeA class.
 	// Initialize an empty linked list, consisting of NodeA nodes.
diff --git a/labs/list_implementation/checkpoint3 b/labs/list_implementation/checkpoint3
new file mode 100755
index 0000000..53628bd
Binary files /dev/null and b/labs/list_implementation/checkpoint3 differ
diff --git a/labs/list_implementation/checkpoint3.cpp b/labs/list_implementation/checkpoint3.cpp
index 6474b38..a14e799 100644
--- a/labs/list_implementation/checkpoint3.cpp
+++ b/labs/list_implementation/checkpoint3.cpp
@@ -15,6 +15,51 @@ public:
 // this function returns a pointer pointing to the head node of the merged list.
 template <class T>
 Node<T>* mergeLists(Node<T>* head_A, Node<T>* head_B) {
+    // If one list is empty, return the other
+    if (!head_A) return head_B;
+    if (!head_B) return head_A;
+
+    // Decide the new head by comparing the first elements
+    Node<T>* head = nullptr;
+    Node<T>* tail = nullptr;
+
+    // Pick whichever head is smaller as the new head
+    if (head_A->value < head_B->value) {
+        head = head_A;
+        head_A = head_A->next;
+    } else {
+        head = head_B;
+        head_B = head_B->next;
+    }
+    // At this point, 'head' is the first node of the merged list
+    head->prev = nullptr; // new head has no previous
+    tail = head;
+
+    // Continue merging while both lists have nodes
+    while (head_A && head_B) {
+        if (head_A->value < head_B->value) {
+            tail->next = head_A;
+            head_A->prev = tail;
+            tail = tail->next;
+            head_A = head_A->next;
+        } else {
+            tail->next = head_B;
+            head_B->prev = tail;
+            tail = tail->next;
+            head_B = head_B->next;
+        }
+    }
+
+    // Append any remaining nodes from A or B
+    if (head_A) {
+        tail->next = head_A;
+        head_A->prev = tail;
+    } else if (head_B) {
+        tail->next = head_B;
+        head_B->prev = tail;
+    }
+
+    return head;
 }
 
 int main() {
diff --git a/labs/list_implementation/dslist.h b/labs/list_implementation/dslist.h
index c59ef55..eabe73b 100644
--- a/labs/list_implementation/dslist.h
+++ b/labs/list_implementation/dslist.h
@@ -131,19 +131,32 @@ dslist<T>& dslist<T>::operator= (const dslist<T>& old) {
 
 template <class T>
 void dslist<T>::push_front(const T& v) {
-
-
-
-
-
+  Node<T>* newp = new Node<T>(v);
+  // if list is empty
+  if (!head_) {
+    head_ = newp;
+    tail_ = newp;
+  } else {
+    newp->next_ = head_;
+    head_->prev_ = newp;
+    head_ = newp;
+  }
+  ++size_;
 }
 
 template <class T>
 void dslist<T>::pop_front() {
-
-
-
-
+  assert(head_ != NULL); // list must not be empty
+  Node<T>* temp = head_;
+  head_ = head_->next_;
+  if (head_) {
+    head_->prev_ = NULL;
+  } else {
+    // list becomes empty
+    tail_ = NULL;
+  }
+  delete temp;
+  --size_;
 }
 
 template <class T>
@@ -163,11 +176,17 @@ void dslist<T>::push_back(const T& v) {
 
 template <class T>
 void dslist<T>::pop_back() {
-
-
-
-
-
+  assert(tail_ != NULL); // list must not be empty
+  Node<T>* temp = tail_;
+  tail_ = tail_->prev_;
+  if (tail_) {
+    tail_->next_ = NULL;
+  } else {
+    // list becomes empty
+    head_ = NULL;
+  }
+  delete temp;
+  --size_;
 }
 
 // do these lists look the same (length & contents)?
@@ -186,7 +205,7 @@ bool operator== (dslist<T>& left, dslist<T>& right) {
 
 template <class T>
 bool operator!= (dslist<T>& left, dslist<T>& right){ return !(left==right); }
-template <class T>
+template <class T>
 typename dslist<T>::iterator dslist<T>::erase(iterator itr) {
   assert (size_ > 0);
   --size_;
@@ -256,13 +275,15 @@ void dslist<T>::copy_list(const dslist<T>& old) {
 
 template <class T>
 void dslist<T>::destroy_list() {
-
-
-
-
-
-
-
+  Node<T>* current = head_;
+  while (current) {
+    Node<T>* next = current->next_;
+    delete current;
+    current = next;
+  }
+  head_ = NULL;
+  tail_ = NULL;
+  size_ = 0;
 }
 
 #endif