09 Sept 2026•Go / Python / TypeScript•Easy

N-th Tribonacci Number

Compute the sequence where each term is the sum of the previous three terms.

View original LeetCode question

Iterate from the three base values while retaining only the latest three terms.

complexity

O(n) time and O(1) space.

solution files

Go n-th-tribonacci-number/solution.go
Python n-th-tribonacci-number/solution.py
TypeScript n-th-tribonacci-number/solution.ts

Solution files

Go•n-th-tribonacci-number/solution.go

package main

func tribonacci(n int) int {
	if n == 0 {
		return 0
	}
	first, second, third := 0, 1, 1
	for index := 3; index <= n; index++ {
		first, second, third = second, third, first+second+third
	}
	return third
}

Python•n-th-tribonacci-number/solution.py

class Solution:
    def tribonacci(self, n: int) -> int:
        if n == class="syntax-number">0: return class="syntax-number">0
        first, second, third = class="syntax-number">0, class="syntax-number">1, class="syntax-number">1
        for _ in range(class="syntax-number">3, n + class="syntax-number">1): first, second, third = second, third, first + second + third
        return third

TypeScript•n-th-tribonacci-number/solution.ts

function tribonacci(n: number): number {
  if (n === class="syntax-number">0) return class="syntax-number">0; if (n < class="syntax-number">3) return class="syntax-number">1;
  let first = class="syntax-number">0; let second = class="syntax-number">1; let third = class="syntax-number">1;
  for (let index = class="syntax-number">3; index <= n; index += class="syntax-number">1) [first, second, third] = [second, third, first + second + third];
  return third;
}