tribonacci.java

/*    Tribonacci Series:
   Tribonacci series is a generalisation of Fibonacci series where current element(greater than 0)
   is the sum of preceding three elements,
   i.e. T(n)=T(n-1)+T(n-2)+T(n-3).

      Approach:

   The sum of three preceding variables will be stored in "sum" variable.
   Variable "first" will be overrided by "second" which in turn will be overrided by "third" which
   will be overrided by "sum".
   This process will continue till n terms.  */

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        long num;
        System.out.println("Enter the number upto which the series is to be printed");
        num = scan.nextLong();
        printTribonacci(num);
    }

    public static void printTribonacci(long num) {
        long first = 0, second = 0, third = 1, sum = 0, count = 0;
        while (num > 0) {
            count++;
            if (count == 1)
                System.out.print(0);
            else if (count == 2)
                System.out.print(", " + 0);
            else if (count == 3)
                System.out.print(", " + 1);
            else {
                sum = first + second + third;
                System.out.print(", " + sum);
                //Storing the values of succeeding terms in respective variables.
                first = second;
                second = third;
                third = sum;
            }
            num--;    //Decreasing the value of total number of terms by one after each iteration.
        }
    }
}

 /*                                              OUTPUT:
 Test Case 1:
 Enter the number upto which the series is to be printed
 23
 0, 0, 1, 1, 2, 4, 7, 13, 24, 44, 81, 149, 274, 504, 927, 1705, 3136, 5768, 10609, 19513, 35890, 66012, 121415

 Space Complexity: O(1)
 Time Complexity: O(n)
 */