# 1137. N-th Tribonacci Number """ the tribonacci sequence t^n is defined as follows t0 = 0, t1 = 1, t2 = 1, & tn+3 = tn + tn+1 + tn+2 for n >= 0 given n, return value of tn eg. n = 4, output: 4 t3 = 0 + 1 + 1 = 2 t4 = 1 + 1 + 2 = 4 """ class Solution(object): def tribonacci(self, n): """ :type n: int :rtype: int """ a, b, c = 1, 0, 0 for _ in range(n): a, b, c = b, c, a + b + c return c if __name__ == "__main__": obj = Solution() print(obj.tribonacci(4)) print(obj.tribonacci(25))