The Tribonacci sequence Tn is defined as follows:

T0 = 0, T1 = 1, T2 = 1, and Tn+3 = Tn + Tn+1 + Tn+2 for n >= 0.

Given n, return the value of Tn.

Example 1:

Input: n = 4 Output: 4 Explanation: T_3 = 0 + 1 + 1 = 2 T_4 = 1 + 1 + 2 = 4

class Solution:
    def tribonacci(self, n: int) -> int:
        dp = {0: 0, 1: 1, 2: 1}
        def dfs(i):
            if i in dp:
                return dp[i]
            dp[i] = dfs(i - 1) + dfs(i - 2) + dfs(i - 3)
            return dp[i]
        
        return dfs(n)

Solution().tribonacci(4)

4