diff --git a/03-lists/.idea/vcs.xml b/03-lists/.idea/vcs.xml
new file mode 100644
index 0000000..6c0b863
--- /dev/null
+++ b/03-lists/.idea/vcs.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$/.." vcs="Git" />
+  </component>
+</project>
\ No newline at end of file
diff --git a/03-lists/national_parks.txt b/03-lists/national_parks.txt
new file mode 100644
index 0000000..8ecbe22
--- /dev/null
+++ b/03-lists/national_parks.txt
@@ -0,0 +1,20 @@
+MOJ CA 1994 Mojave National Preserve; Spectacular Landscape in Absolute Solitude
+YOS CA 1890 Yosemite National Park; A Land of Giants
+LAS CA 1916 Lassen Volcanic National Park; Bubbling Below the Surface
+PRE CA 1962 Point Reyes National Seashore; Sky Above, Sea Beyond
+BRC UT 1928 Bryce Canyon National Park; Pillars of Stone
+DEV CA 1911 Devils Postpile National Monument; A Geologic Gem
+MUW CA 1908 Muir Woods National Monument; John Muir’s Cathedral
+CAL UT 1964 Canyonlands National Park; The Heart of the High Desert
+GLA MT 1910 Glacier National Park; Reflections of the Past
+ALC CA 1934 Alcatraz Island; Landmark Unlocked
+YEL WY 1872 Yellowstone National Park; Otherworldly on Earth
+ROC CO 1915 Rocky Mountain National Park; On Top of the World
+CRA OR 1902 Crater Lake National Park; Deep and Pristine Waters
+PIN CA 2013 Pinnacles National Park; Spectacular Remains of an Ancient Volcano
+DEN AK 1980 Denali National Park and Preserve; Beyond the Mountain
+ZIO UT 1919 Zion National Park; An Oasis Amidst the Desert
+JOS CA 1994 Joshua Tree National Park; The Outer Limits of Reality
+GRC AZ 1908 Grand Canyon National Park; A Sight Beyond Words
+ARC UT 1929 Arches National Park; Windows to the Sky
+DEA CA 1994 Death Valley National Park; A Land of Extremes
\ No newline at end of file
diff --git a/04-dl-lists/CMakeLists.txt b/04-dl-lists/CMakeLists.txt
index 4408395..8c97fd2 100644
--- a/04-dl-lists/CMakeLists.txt
+++ b/04-dl-lists/CMakeLists.txt
@@ -4,4 +4,6 @@ project(04_dl_lists)
 set(CMAKE_CXX_STANDARD 20)
 
 add_executable(04_dl_lists main.cpp
-        StudentList.cpp)
+        StudentList.cpp
+        LinkedList.cpp
+        Park.cpp)
diff --git a/04-dl-lists/LinkedList.cpp b/04-dl-lists/LinkedList.cpp
new file mode 100644
index 0000000..253621a
--- /dev/null
+++ b/04-dl-lists/LinkedList.cpp
@@ -0,0 +1,186 @@
+// Implementation file for the LinkedList class
+// Written By: Iurii Tatishchev
+// Reviewed & Modified by: Iurii Tatishchev
+// IDE: CLion
+
+#include <iostream>
+#include "LinkedList.h"
+
+using namespace std;
+
+// **************************************************
+// Constructor
+// This function allocates and initializes a sentinel node
+//      A sentinel (or dummy) node is an extra node added before the first data record.
+//      This convention simplifies and accelerates some list-manipulation algorithms,
+//      by making sure that all links can be safely dereferenced and that every list
+//      (even one that contains no data elements) always has a "first" node.
+// **************************************************
+LinkedList::LinkedList() {
+    head = new ListNode; // head points to the sentinel node
+    head->setNext(head);
+    head->setPrev(head);
+    length = 0;
+}
+
+// **************************************************
+// The insertNode function inserts a new node in a
+// sorted linked list
+// **************************************************
+void LinkedList::insertNode(Park dataIn) {
+    ListNode *newNode;  // A new node
+    ListNode *pCur;     // To traverse the list
+    ListNode *pPre;     // The previous node
+
+    // Allocate a new node and store num there.
+    newNode = new ListNode(dataIn);
+
+    // Initialize pointers
+    pCur = head->getNext();
+
+    // Find location: skip all nodes whose code is less than dataIn's code
+    while (pCur != head && newNode->getData().getCode() > pCur->getData().getCode()) {
+        pCur = pCur->getNext();
+    }
+
+    // Insert the new node between pPre and pCur
+    pPre = pCur->getPrev();
+    pPre->setNext(newNode);
+    newNode->setNext(pCur);
+
+    pCur->setPrev(newNode);
+    newNode->setPrev(pPre);
+
+
+    // Update the counter
+    length++;
+}
+
+// **************************************************
+// The deleteNode function searches for a node
+// in a sorted linked list; if found, the node is
+// deleted from the list and from memory.
+// **************************************************
+bool LinkedList::deleteNode(string target) {
+    ListNode *pCur;       // To traverse the list
+    ListNode *pPre;       // To point to the previous node
+    bool deleted = false;
+
+    // Initialize pointers
+    pCur = head->getNext();
+
+    // Find node containing the target: Skip all nodes whose gpa is less than the target
+    while (pCur != head && pCur->getData().getCode() < target) {
+        pCur = pCur->getNext();
+    }
+
+    // If found, delete the node
+    if (pCur->getData().getCode() == target) {
+        pPre = pCur->getPrev();
+        pPre->setNext(pCur->getNext()); // Set next of prev
+        pCur->getNext()->setPrev(pPre); // Set prev of next
+
+        delete pCur;
+        deleted = true;
+        length--;
+    }
+    return deleted;
+}
+
+// **************************************************
+// displayListForw() shows the value
+// stored in each node of the linked list
+// pointed to by head, except the sentinel node,
+// from head to tail (ascending order).
+// **************************************************
+void LinkedList::displayListForw() const {
+    ListNode *pCur;  // To move through the list
+
+    // Position pCur: skip the head of the list.
+    pCur = head->getNext();
+
+    // While pCur points to a node, traverse the list.
+    while (pCur != head) {
+        // Display the value in this node.
+        pCur->getData().hDdisplay();
+
+        // Move to the next node.
+        pCur = pCur->getNext();
+    }
+    cout << endl;
+}
+
+// **************************************************
+// displayListBack() shows the value
+// stored in each node of the linked list
+// pointed to by head, except the sentinel node.
+// from tail to head (descending order).
+// **************************************************
+void LinkedList::displayListBack() const {
+    ListNode *pCur;  // To move through the list
+
+    // Position pCur: skip the head of the list.
+    pCur = head->getPrev();
+
+    // While pCur points to a node, traverse the list.
+    while (pCur != head) {
+        // Display the value in this node.
+        pCur->getData().hDdisplay();
+
+        // Move to the next node.
+        pCur = pCur->getPrev();
+    }
+
+    cout << endl;
+}
+
+
+// **************************************************
+// The searchList function looks for a target college
+// in the sorted linked list: if found, returns true
+// and copies the data in that node to the output parameter
+// **************************************************
+bool LinkedList::searchList(const string& target, Park &dataOut) const {
+    bool found = false; // assume target not found
+    ListNode *pCur;         // To move through the list
+
+    // Position pCur: skip the head of the list.
+    pCur = head->getNext();
+    // Find location: skip all nodes whose code is less than target
+    while (pCur != head && pCur->getData().getCode() < target) {
+        pCur = pCur->getNext();
+    }
+
+    // If found, copy data to the output parameter, and change the flag to true
+    if (pCur != head && pCur->getData().getCode() == target) {
+        dataOut = pCur->getData();
+        found = true;
+    }
+
+    return found;
+}
+
+// **************************************************
+// Destructor
+// This function deletes every node in the list.
+// **************************************************
+LinkedList::~LinkedList() {
+    ListNode *pCur;     // To traverse the list
+    ListNode *pNext;    // To hold the address of the next node
+
+    // Position nodePtr: skip the head of the list
+    pCur = head->getNext();
+    // While pCur is not at the end of the list...
+    while (pCur != head) {
+        // Save a pointer to the next node.
+        pNext = pCur->getNext();
+
+        // Delete the current node.
+        delete pCur;
+
+        // Position pCur at the next node.
+        pCur = pNext;
+    }
+
+    delete head; // delete the sentinel node
+}
diff --git a/04-dl-lists/LinkedList.h b/04-dl-lists/LinkedList.h
new file mode 100644
index 0000000..edb636c
--- /dev/null
+++ b/04-dl-lists/LinkedList.h
@@ -0,0 +1,37 @@
+// Specification file for the LinkedList class
+// Written By: Iurii Tatishchev
+// Reviewed by: Iurii Tatishchev
+// IDE: CLion
+
+#ifndef LINKED_LIST_H
+#define LINKED_LIST_H
+
+#include "ListNode.h"
+
+class LinkedList {
+private:
+    ListNode *head;
+    int length;
+
+public:
+    LinkedList();   // constructor
+    ~LinkedList();  // destructor
+
+    // Linked list operations
+    int getLength() const { return length; }
+
+    bool isEmpty() const { return length == 0; }
+
+    void insertNode(Park);
+
+    bool deleteNode(string);
+
+    void displayListForw() const;
+
+    void displayListBack() const;
+
+    bool searchList(const string &, Park &) const;
+};
+
+#endif
+
diff --git a/04-dl-lists/ListNode.h b/04-dl-lists/ListNode.h
new file mode 100644
index 0000000..7af926d
--- /dev/null
+++ b/04-dl-lists/ListNode.h
@@ -0,0 +1,43 @@
+// Specification file for the ListNode class
+// Written By: Iurii Tatishchev
+// Reviewed & Modified by: Iurii Tatishchev
+// IDE: CLion
+
+#ifndef LISTNODE_H
+#define LISTNODE_H
+
+#include <iostream>
+#include "Park.h"
+
+class ListNode {
+private:
+    Park data;         // store data
+    ListNode *forw;    // a pointer to the next node in the list
+    ListNode *back;    // a pointer to the previous node in the list
+public:
+    // Constructor
+    ListNode() { forw = back = nullptr; }
+
+    ListNode(const Park &dataIn, ListNode *forw = nullptr, ListNode *back = nullptr) {
+        data = dataIn;
+        this->forw = forw;
+        this->back = back;
+    }
+
+    // setters
+    // set the forw pointer
+    void setNext(ListNode *nextPtr) { forw = nextPtr; }
+    // set the back pointer
+    void setPrev(ListNode *prevPtr) { back = prevPtr; }
+
+    // getters
+    // return pointer in the next node
+    ListNode *getNext() const { return forw; }
+    // return pointer in the previous node
+    ListNode *getPrev() const { return back; }
+
+    // return data object in the listnode
+    Park& getData() { return data; }
+};
+
+#endif
diff --git a/04-dl-lists/Park.cpp b/04-dl-lists/Park.cpp
new file mode 100644
index 0000000..7c32cf9
--- /dev/null
+++ b/04-dl-lists/Park.cpp
@@ -0,0 +1,60 @@
+// Implementation file for the Park class
+// Written By: Iurii Tatishchev
+// Reviewed By: Iurii Tatishchev
+// IDE: CLion
+
+
+#include <iostream>
+#include <iomanip>
+#include <string>
+
+#include "Park.h"
+
+using namespace std;
+
+// **************************************************
+// Constructor
+// **************************************************
+Park::Park() {
+    code = "";
+    state = "";
+    name = "";
+    description = "";
+    year = -1;
+}
+
+// **************************************************
+// Overloaded Constructor
+// **************************************************
+Park::Park(string cd, string st, string nm, string dsc, int yr) {
+    code = cd;
+    state = st;
+    name = nm;
+    description = dsc;
+    year = yr;
+}
+
+// ***********************************************************
+// Displays the values of a Park object member variables
+// on one line (horizontal display)
+// ***********************************************************
+void Park::hDdisplay() const {
+    cout << code << " ";
+    cout << state << " ";
+    cout << year << " ";
+    cout << name << " ";
+    //cout << "(" << description << ")";
+    cout << endl;
+}
+
+// ***********************************************************
+// Displays the values of a Park object member variables
+// one per line (vertical display)
+// ***********************************************************
+void Park::vDisplay() const {
+    cout << name << endl;
+    cout << description << endl;
+    cout << state << endl;
+    cout << year << endl;
+}
+
diff --git a/04-dl-lists/Park.h b/04-dl-lists/Park.h
new file mode 100644
index 0000000..3cdcf7c
--- /dev/null
+++ b/04-dl-lists/Park.h
@@ -0,0 +1,64 @@
+// Specification file for the Park class
+// Written By: Iurii Tatishchev
+// Reviewed by: Iurii Tatishchev
+// IDE: CLion
+
+#ifndef PARK_H
+#define PARK_H
+
+// #include<iostream>
+#include<string>
+// #include<cstdlib>
+
+// using namespace std;
+// ^^^^^ This statement
+// in a header file of a complex project could create
+// namespace management problems for the entire project
+// (such as name collisions).
+// Do not write using namespace at the top level in a header file!
+
+using std::string;
+
+class Park {
+private:
+    string code;  // the unique park identifier
+    string state;
+    string name;
+    string description;
+    int year;
+
+public:
+    // constructors
+    Park();
+
+    Park(string, string, string, string, int);
+
+    // setters
+    void setCode(string cd) { code = cd; }
+
+    void setState(string st) { state = st; }
+
+    void setName(string nm) { name = nm; }
+
+    void setDesc(int dsc) { description = dsc; }
+
+    void setYear(int yr) { year = yr; }
+
+    // getters
+    string getCode() const { return code; }
+
+    string getState() const { return state; }
+
+    string getName() const { return name; }
+
+    string getDesc() const { return description; }
+
+    int getYear() const { return year; }
+
+    // other functions
+    void hDdisplay() const;
+
+    void vDisplay() const;
+};
+
+#endif
diff --git a/04-dl-lists/main.cpp b/04-dl-lists/main.cpp
index 0249173..ff4d0d7 100644
--- a/04-dl-lists/main.cpp
+++ b/04-dl-lists/main.cpp
@@ -1,70 +1,147 @@
 /*
-CIS 22C: Sorted Circular Doubly-Linked List with Sentinel Node
+ Sorted Circular Doubly-Linked List with Sentinel Node
 
-This program:
-- Creates a sorted linked list (student name and gpa). The list is sorted in ascending order by name. Assume name is a unique identifier.
-- Displays the list forwards(A to Z)
-- Displays the list backwards(Z to A)
+ Build and procees a sorted linked list of Park objects.
+ The list is sorted in ascending order by the Park code, a unique identifier.
 
-Your task is to finish writing the following three functions:
-- default constructor (reuse code from your previous lab)
-- `displayListBack()`  (reuse code from your previous lab)
-- `insertNode()`  - change this function to reject duplicates. Assume `name` is a unique key.
-
- Written by: Iurii Tatishchev
- Reviewed by: Iurii Tatishchev
- IDE: CLion
+// Written by: Iurii Tatishchev
+// Reviewed & Modified by: Iurii Tatishchev
+// IDE: CLion
 
  */
 
 #include <iostream>
+#include <fstream>
 #include <sstream>
-#include "StudentList.h"
+#include <string>
+#include <cctype>  //  toupper()
+#include "LinkedList.h"
 
 using namespace std;
 
-void buildList(StudentList &);
+void buildList(const string &filename, LinkedList &list);
+
+void deleteManager(LinkedList &list);
+
+void searchManager(const LinkedList &list);
+
+void displayManager(const LinkedList &list);
 
 int main() {
-    // Define a StudentList object
-    StudentList list;
+    string inputFileName = "national_parks.txt";
+    LinkedList list;
 
-    buildList(list); // insert data into the list
-    cout << "The number of elements in the list is " << list.getCount() << "." << endl;
-    string answer;
-    cout << "Insert [Y/N]? ";
-    cin >> answer;
-    if (answer == "Y" || answer == "y") {
-        Student s;
-        cout << "Enter gpa then enter name:" << endl;
-        cin >> s.gpa >> s.name;
-        if (!list.insertNode(s)) {
-            cout << s.name << " - rejected: duplicate key!" << endl;
-        }
-        cout << "The number of elements in the list is " << list.getCount() << "." << endl;
-    }
-    cout << endl;
-    list.displayListForw();
-    list.displayListBack();
+    buildList(inputFileName, list);
+    displayManager(list);
+    searchManager(list);
+    deleteManager(list);
+    displayManager(list);
     return 0;
 }
 
-/* **************************************************
-This function builds a sorted linked list with data from the keyboard.
-The list is sorted in ascending order by the students' names.
-It calls the insertNode() function that inserts the new data at the right location in the linked list.
-An input line contains the gpa of a student follow by its name (assume it is a single word name)
-To stop reading enter "#"
-************************************************** */
-void buildList(StudentList &list) {
+/*
+ This function reads data about national parks from a file and inserts them
+ into a sorted linked list. The list is sorted in ascending order by code.
+ */
+void buildList(const string &filename, LinkedList &list) {
+    ifstream inputFile(filename);
+    cout << "Reading data from \"" << filename << "\"" << endl;
+
+    if (!inputFile) {
+        cout << "Error opening the input file: \"" << filename << "\"" << endl;
+        exit(EXIT_FAILURE);
+    }
+
     string line;
-    getline(cin, line);
-    while (line != "#") {
-        stringstream temp(line); // create a stringstream named temp with data from line
-        Student newStu;
-        temp >> newStu.gpa;  // read gpa from temp
-        temp >> newStu.name; // read name from temp
-        list.insertNode(newStu);
-        getline(cin, line);
+    while (getline(inputFile, line)) {
+        int year;
+        string code, name, state, dsc;
+
+        stringstream temp(line);   // create temp with data from line
+        temp >> code;              // read from temp
+        temp >> state;
+        temp >> year;
+        temp.ignore();             // to ignore space in front of name
+        getline(temp, name, ';');   // stop reading name at ';'
+        temp.ignore();             // to ignore space in front of description
+        getline(temp, dsc);
+        // create a Park object and initialize it with data from file
+        Park aPark(code, state, name, dsc, year);
+        list.insertNode(aPark);
+    }
+
+    inputFile.close();
+}
+
+/*
+ Delete manager: delete items from the list until the user enters Q to quit
+ deleting
+ Input Parameter: list
+ */
+void deleteManager(LinkedList &list) {
+    string targetCode;
+
+    cout << endl << " Delete" << endl;
+    cout << "=======" << endl;
+
+    while (targetCode != "Q") {
+        cout << "Enter a park code (or Q to stop deleting):" << endl;
+        getline(cin, targetCode);
+        targetCode[0] = toupper(targetCode[0]);
+        if (targetCode != "Q") {
+            if (list.deleteNode(targetCode))
+                cout << "    " << targetCode << " has been deleted!" << endl;
+            else
+                cout << "Park \"" << targetCode << "\" was not found in this list." << endl;
+        }
+    }
+    cout << "___________________END DELETE SECTION_____" << endl;
+}
+
+/*
+ Search manager: search the list until the user enters Q to quit searching
+ Input Parameter: list
+ */
+void searchManager(const LinkedList &list) {
+    string targetCode = "";
+    Park aPark;
+
+    cout << endl << " Search" << endl;
+    cout << "=======" << endl;
+
+    while (targetCode != "Q") {
+        cout << "Enter a park code (or Q to stop searching):" << endl;
+        getline(cin, targetCode);
+        targetCode[0] = toupper(targetCode[0]);
+        if (targetCode != "Q") {
+            if (list.searchList(targetCode, aPark))
+                aPark.vDisplay();
+            else
+                cout << "Park \"" << targetCode << "\" was not found in this list." << endl;
+        }
+    }
+    cout << "___________________END SEARCH SECTION _____" << endl;
+}
+
+/*
+Display manager:
+ - displays the number of national parks in this list
+ - calls the displayListForw()/displayListBack() function upon request
+Input Parameter: list
+ */
+void displayManager(const LinkedList &list) {
+    string action;
+
+    cout << "Number of National Parks in this list: " << list.getLength() << endl;
+    cout << "Display list [F/B/N]?" << endl;
+    getline(cin, action);
+
+    switch (toupper(action[0])) {
+        case 'F':
+            list.displayListForw();
+            break;
+        case 'B':
+            list.displayListBack();
+            break;
     }
 }
diff --git a/04-dl-lists/national_parks.txt b/04-dl-lists/national_parks.txt
new file mode 100644
index 0000000..8ecbe22
--- /dev/null
+++ b/04-dl-lists/national_parks.txt
@@ -0,0 +1,20 @@
+MOJ CA 1994 Mojave National Preserve; Spectacular Landscape in Absolute Solitude
+YOS CA 1890 Yosemite National Park; A Land of Giants
+LAS CA 1916 Lassen Volcanic National Park; Bubbling Below the Surface
+PRE CA 1962 Point Reyes National Seashore; Sky Above, Sea Beyond
+BRC UT 1928 Bryce Canyon National Park; Pillars of Stone
+DEV CA 1911 Devils Postpile National Monument; A Geologic Gem
+MUW CA 1908 Muir Woods National Monument; John Muir’s Cathedral
+CAL UT 1964 Canyonlands National Park; The Heart of the High Desert
+GLA MT 1910 Glacier National Park; Reflections of the Past
+ALC CA 1934 Alcatraz Island; Landmark Unlocked
+YEL WY 1872 Yellowstone National Park; Otherworldly on Earth
+ROC CO 1915 Rocky Mountain National Park; On Top of the World
+CRA OR 1902 Crater Lake National Park; Deep and Pristine Waters
+PIN CA 2013 Pinnacles National Park; Spectacular Remains of an Ancient Volcano
+DEN AK 1980 Denali National Park and Preserve; Beyond the Mountain
+ZIO UT 1919 Zion National Park; An Oasis Amidst the Desert
+JOS CA 1994 Joshua Tree National Park; The Outer Limits of Reality
+GRC AZ 1908 Grand Canyon National Park; A Sight Beyond Words
+ARC UT 1929 Arches National Park; Windows to the Sky
+DEA CA 1994 Death Valley National Park; A Land of Extremes
\ No newline at end of file