DSA Python Project – To Do List

Program 1

# To-Do List Using Singly Linked List
class Task:
    def __init__(self, task_id, description):
        self.id = task_id
        self.description = description
        self.completed = False
        self.next = None


class ToDoList:
    def __init__(self):
        self.head = None
        self.task_count = 0

    def add_task(self):
        desc = input("Enter task description: ").strip()
        self.task_count += 1
        new_task = Task(self.task_count, desc)

        if self.head is None:
            self.head = new_task
        else:
            temp = self.head
            while temp.next:
                temp = temp.next
            temp.next = new_task

        print("Task added successfully.")

    def display_tasks(self):
        if not self.head:
            print("To-Do List is empty.")
            return

        print("\nTo-Do List:")
        temp = self.head
        while temp:
            status = "[X]" if temp.completed else "[ ]"
            print(f"ID: {temp.id} | {status} {temp.description}")
            temp = temp.next

    def mark_completed(self):
        try:
            task_id = int(input("Enter task ID to mark as completed: "))
        except ValueError:
            print("Invalid input.")
            return

        temp = self.head
        while temp:
            if temp.id == task_id:
                temp.completed = True
                print("Task marked as completed.")
                return
            temp = temp.next

        print(f"Task with ID {task_id} not found.")

    def delete_task(self):
        try:
            task_id = int(input("Enter task ID to delete: "))
        except ValueError:
            print("Invalid input.")
            return

        temp = self.head
        prev = None

        while temp and temp.id != task_id:
            prev = temp
            temp = temp.next

        if not temp:
            print(f"Task with ID {task_id} not found.")
            return

        if not prev:
            self.head = temp.next
        else:
            prev.next = temp.next

        print("Task deleted successfully.")


def main():
    todo_list = ToDoList()

    while True:
        print("\n----- To-Do List Menu -----")
        print("1. Add Task")
        print("2. Display Tasks")
        print("3. Mark Task as Completed")
        print("4. Delete Task")
        print("5. Exit")
        print("---------------------------")
        choice = input("Enter your choice: ").strip()

        if choice == '1':
            todo_list.add_task()
        elif choice == '2':
            todo_list.display_tasks()
        elif choice == '3':
            todo_list.mark_completed()
        elif choice == '4':
            todo_list.delete_task()
        elif choice == '5':
            print("Exiting program.")
            break
        else:
            print("Invalid choice. Try again.")


if __name__ == "__main__":
    main()