Isaac Emmanuel
09 Sept 2026•EasyGo / Python / TypeScript

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
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 == 0: return 0
        first, second, third = 0, 1, 1
        for _ in range(3, n + 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 === 0) return 0; if (n < 3) return 1;
  let first = 0; let second = 1; let third = 1;
  for (let index = 3; index <= n; index += 1) [first, second, third] = [second, third, first + second + third];
  return third;
}