Tribonacci Number using Memoization

The Tribonacci sequence Tn is defined as follows:

T(0) = 0, T(1) = 1, T(2) = 1
T(n + 3) = T(n) + T(n + 1) + T(n + 2) for n >= 0.

Given n, calculate T(n).

Example 1:

Input: n = 2
Output: 1

Example 2:

Input: n = 3
Output: 2

Example 3:

Input: n = 4
Output: 4