1137. N-th Tribonacci Number

{leetcode}/problems/n-th-tribonacci-number/[LeetCode - N-th Tribonacci Number^]

The Tribonacci sequence T_n is defined as follows:

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

Given n, return the value of T_n.

Example 1:

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

Example 2:

Input: n = 25
Output: 1389537

Constraints:

0 ⇐ n ⇐ 37
The answer is guaranteed to fit within a 32-bit integer, ie. answer ⇐ 2^31 - 1.

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