Practice - Tribonacci Number

The Tribonacci sequence is defined as $T_0 = 0$, $T_1 = 1$, $T_2 = 1$, and $T_n = T_{n-1} + T_{n-2} + T_{n-3}$ for $n \geq 3$.

Given $n$, compute $T_n$. This is like Fibonacci but with three terms instead of two.

Hint: use dynamic programming with $O(n)$ time and $O(1)$ space by tracking only the last three values.