Tribonacci Word

• Difficulty Level : Basic
• Last Updated : 30 Apr, 2021

Like Fibonacci word, a Tribonacci word. is a specific sequence of digits. The Tribonacci word is formed by repeated concatenation in the same way that the Fibonacci word is formed by repeated addition. But unlike the fibonacci word, Tribonacci word is formed by repeated addition of last three terms and it has its first three terms different from each other.

In Tribonacci word,
S(0) = 1,
S(1) = 12,
S(2) = 1213,
S(3) = 1213121
.....
where S(n) = S(n-1) + S(n-2) + S(n-3) and +
represents the concatenation of
strings.

The task is to find nth Tribonacci word for a given number n.
Examples:

Input : n = 4
Output : S(4) = 1213121121312

Input : n = 3
Output : S(3) = 1213121

Just like in program of Fibonacci word, we use the iterative concept of finding nth Fibonacci word here for finding nth Tribonacci word we can use the iterative concept. So for finding nth Tribonacci word we will take three string Sn_1, Sn_2 and Sn_3 which represent S(n-1), S(n-2) and S(n-3) respectively and on each iteration we will update tmp = Sn_3, Sn_3 = Sn_3 + Sn_2 + Sn_1, Sn_1 = Sn_2 and Sn_2 = tmp in this way we can find nth tribonacci word.

C++

 // C++ program for nth Fibonacci word#include using namespace std; // Returns n-th Tribonacci wordstring tribWord(int n) {  string Sn_1 = "1";  string Sn_2 = "12";  string Sn_3 = "1213";  string tmp;  for (int i = 3; i <= n; i++) {    tmp = Sn_3;    Sn_3 += (Sn_2 + Sn_1);    Sn_1 = Sn_2;    Sn_2 = tmp;  }   return Sn_3;} // driver programint main() {  int n = 6;  cout << tribWord(n);  return 0;}

Java

 // program for nth Tribonacci wordclass GFG { // Returns n-th Tribonacci wordstatic String tribWord(int n) {    String Sn_1 = "1";    String Sn_2 = "12";    String Sn_3 = "1213";    String tmp;    for (int i = 3; i <= n; i++) {    tmp = Sn_3;    Sn_3 += (Sn_2 + Sn_1);    Sn_1 = Sn_2;    Sn_2 = tmp;    }     return Sn_3;} // Driver codepublic static void main(String[] args) {    int n = 6;    System.out.print(tribWord(n));}}// This code is contributed by Anant Agarwal.

Python3

 # Python3 Program for nth# Tribonacci word # Returns n-th Tribonacci worddef tribWord(n):    Sn_1 = "1"    Sn_2 = "12"    Sn_3 = "1213"    for i in range(3, n+1):        tmp = Sn_3        Sn_3 += (Sn_2 + Sn_1)        Sn_1 = Sn_2        Sn_2 = tmp     return Sn_3 # Driver coden = 6print(tribWord(n)) # This code is contributed By Anant Agarwal.

C#

 // C# program for nth Tribonacci wordusing System; class GFG {     // Returns n-th Tribonacci word    static string tribWord(int n)    {        string Sn_1 = "1";        string Sn_2 = "12";        string Sn_3 = "1213";        string tmp;                 for (int i = 3; i <= n; i++) {            tmp = Sn_3;            Sn_3 += (Sn_2 + Sn_1);            Sn_1 = Sn_2;            Sn_2 = tmp;        }             return Sn_3;    }         // Driver code    public static void Main() {                 int n = 6;                 Console.WriteLine(tribWord(n));    }} // This code is contributed by vt_m.



Javascript



Output:

12131211213121213121121312131211213121213121

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