n_th_tribonacci_number.py

class Solution(object):
    def tribonacci(self, n):
        """
        :type n: int
        :rtype: int
        """
        if n == 0:
            return 0
        if n == 1:
            return 1
        if n == 2:
            return 1
        dp = [0 for _ in range(n + 1)]
        dp[0] = 0
        dp[1] = 1
        dp[2] = 1
        for i in range(3, n + 1):
            dp[i] = dp[i - 1] + dp[i - 2] + dp[i - 3]
        return dp[-1]