1137

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.

Solution

Here's a brief overview of what the code does:

1. tribWithMemo function: This function calculates the nth number in the Tribonacci sequence using memoization to optimize the calculation. Memoization is a technique where you store the results of expensive function calls and reuse the cached result when the same inputs occur again.

2. tribonacci function: This function initializes a map with the base cases of the Tribonacci sequence (0:0, 1:1, 2:1) and then calls the tribWithMemo function to calculate the nth number in the sequence.