Question

Write a program of doubly Circular linked list to maintain records of employees. Take employee ID, name and salary as data of each employee. Search a particular record on ID and display the previous and next records as well. Whichever ID it give, it should display all the records because of being circular.

Code needed in Java.

Answer 1

I have implemented Doubly circular linkedlist with the following methods::

1> public void insertFirst(int empId, String empName, long empSalary) : This method add employee at the first position in the doubly circular linkedlist.

2> public void insertLast(int empId, String empName, long empSalary) : This method add employee at the last position in the doubly circular linkedlist.

3> public void displayList() : This method display each employee detail from the linkedlist.

4> public void searchEmployeeById(int empId) : This method search the employee with empId.

5> public void displaySearchedEmployeeDetail(Employee searchedEmployee) : This method display searched employee detail with its previous and next employee.

Here, DoublyCircularLinkedList class contain Employee class which represents as a node in the doubly circular linked list.

Program:-

// This class represents DoublyCircularLinkedList
class DoublyCircularLinkedList{
    
    // point to the first Employee (firs node of linkedlist)
    Employee start;
    
    // This class represents Employee as a node of the linkedlist
    class Employee{
        
        // store employee id
        int empId;
        
        // store employee name;
        String empName;
        
        // store employee salary
        long empSalary;

        // store prev employee detail
        Employee prev;
        
        // store next employee detail
        Employee next;
        
        // constructor which create a node for he linkedlist
        public Employee(int empId, String empName, long empSalary) {
            this.empId = empId;
            this.empName = empName;
            this.empSalary = empSalary;
            this.prev = null;
            this.next = null;
        }
        
    
    }
    
    // This method add the newEmployee at the first of linkedlist
    public void insertFirst(int empId, String empName, long empSalary){
        
        // create employee node for the linkedlist
        Employee newEmployee = new Employee(empId, empName, empSalary);
        
        // if the list is empty make newEmployee as a start node
        if(start == null){
            
            newEmployee.next = newEmployee;
            newEmployee.prev = newEmployee;
            start = newEmployee;
            return;
        }
        
        
        // first get the last node using start
        Employee lastEmployee = start.prev;
        
        // now store start Employee to the next of newEmployee
        newEmployee.next = start;
        
        // point newEmployee to the prev of start employee
        start.prev = newEmployee;

        // point the last node to the prev of newEmployee
        newEmployee.prev = lastEmployee;
        
        // point newEmployee to the next of lastEmployee
        lastEmployee.next = newEmployee;
        
        // finally make the newEmployee as a start Employee
        start = newEmployee;
       
    }
    
    
    // This method add the newEmployee at the last of linkedlist
    public void insertLast(int empId, String empName, long empSalary){
        
        // create employee node for the linkedlist
        Employee newEmployee = new Employee(empId, empName, empSalary);
        
         // if the list is empty make newEmployee as a start node
        if(start == null){
            
            start = newEmployee;
            start.next = start;
            start.prev = start;
            return;
        }
        
        // point to the last node of linkedlist
        Employee lastEmployee = start.prev;
        
        // now store newEmployee to the next of lastEmployee
        lastEmployee.next = newEmployee;
        
        // now store last employee into the prev of newEmployee
        newEmployee.prev = lastEmployee;
        
        // point the start node from the newEmployee
        newEmployee.next = start;
        
        // and at the end, point newEmployee to the prev of start 
        start.prev = newEmployee;
       
    }
    
    
    // This method display the each employee detail
    public void displayList(){
        
        // if list is empty then return from the method
        if(start == null){
            System.out.println("Doubly Circular LinkedList is EMpty!");
            return;
        }
        
        System.out.println("\n--------- Employee Details ---------\n");
        // store start node
        Employee curr = start;
        
        // display each node detail
        while(curr.next != start){
            
            // display employee detail
            System.out.println("Employee id : "+curr.empId);
            System.out.println("Employee Name : "+curr.empName);
            System.out.println("Employee Salary : "+curr.empSalary);
            
            System.out.println("\n\t------||------");
            System.out.println("\tNext Employee");
            System.out.println("\t------||------\n");
            
            // go too the next Employee
            curr = curr.next;
            
        }
        
        // now display the last Employee detail
        System.out.println("Employee id : "+curr.empId);
        System.out.println("Employee Name : "+curr.empName);
        System.out.println("Employee Salary : "+curr.empSalary);
    }
    
    
    // This method search Employee in the list by empId
    public void searchEmployeeById(int empId){
        
        System.out.println("\n ---- Search Employee with "+empId+" empId ----\n");
        // if list is empty then return from the method
        if(start == null){
            System.out.println("Doubly Circular LinkedList is EMpty!");
            return;
        }
        
        // store start node
        Employee curr = start;
        
        boolean flagFound = false;
        // compare empId with each node
        while(curr.next != start){
            
            // compare emp Id
            if(curr.empId == empId){
                flagFound = true;
                break;
            }
            
            // go too the next Employee
            curr = curr.next;
        }
        
        // empId found
        if(flagFound){
            
            // displa searchedEmployee detail with the prev and next employee detail of searchedEmployee
            displaySearchedEmployeeDetail(curr);
            
        }else{
            
            // now compare with last employee
            if(curr.empId == empId){
                
                // displa searchedEmployee detail with the prev and next employee detail of searchedEmployee
                displaySearchedEmployeeDetail(curr);
                
            }else{
                
                System.out.println("Employee does not exist with "+empId+" empId");
            }
        }
    }
    
    
    // This method display the searched Employee deatail and also display the prev and next employee detail
    public void displaySearchedEmployeeDetail(Employee searchedEmployee){
        
        // display the searchedEmployee employee record
        System.out.println("Searched Employee id : "+searchedEmployee.empId);
        System.out.println("Searched Employee Name : "+searchedEmployee.empName);
        System.out.println("Searched Employee Salary : "+searchedEmployee.empSalary);
            
        System.out.println("\n\t----------||----------");
        System.out.println("\t"+searchedEmployee.empName+"'s Previous Employee");
        System.out.println("\t----------||----------\n");
            
        // display the prev employee record
        System.out.println("Employee id : "+searchedEmployee.prev.empId);
        System.out.println("Employee Name : "+searchedEmployee.prev.empName);
        System.out.println("Employee Salary : "+searchedEmployee.prev.empSalary);
            
        System.out.println("\n\t----------||----------");
        System.out.println("\t"+searchedEmployee.empName+"'s Next Employee");
        System.out.println("\t----------||----------\n");
            
        // display the next employee record
        System.out.println("Employee id : "+searchedEmployee.next.empId);
        System.out.println("Employee Name : "+searchedEmployee.next.empName);
        System.out.println("Employee Salary : "+searchedEmployee.next.empSalary);
        
    }
}


public class TestDoublyCircularLinkedList {
    
    public static void main(String[] args) {
        
        // create doubly circular linked lisr
        DoublyCircularLinkedList dcll = new DoublyCircularLinkedList();

        // now add the first employee detail
        dcll.insertFirst(1, "Harshal", 100000);
        
        // add the employee details
        dcll.insertLast(2, "Sagar", 50000);
        
        // add the employee details
        dcll.insertLast(3, "Mohan", 10000);
        
        // display all employee details
        dcll.displayList();
        
        // search employee by empId and display next and previous employee also
        dcll.searchEmployeeById(1);
        
    }
    
}

Output:-

I hope you will understand the above program.

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