Introduction

In this blog post, we will explore how to solve the LeetCode problem "1137" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

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 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.

Explanation

Here's an efficient solution to calculate the nth Tribonacci number:

• Iterative Approach: We'll use an iterative approach to calculate the Tribonacci numbers. We will start from the base cases (T0, T1, T2) and iteratively compute subsequent values up to Tn.

• Constant Space Optimization: To optimize space, we will maintain only the last three Tribonacci numbers calculated. These will be updated in each iteration to produce the next number in the sequence.

• Runtime Complexity: O(n), Storage Complexity: O(1)

Code

    def tribonacci(n: int) -> int:
    """
    Calculates the nth Tribonacci number.

    Args:
        n: The index of the Tribonacci number to calculate.

    Returns:
        The nth Tribonacci number.
    """
    if n == 0:
        return 0
    if n == 1 or n == 2:
        return 1

    t0 = 0
    t1 = 1
    t2 = 1

    for _ in range(3, n + 1):
        tn = t0 + t1 + t2
        t0 = t1
        t1 = t2
        t2 = tn

    return t2