1137. N-th Tribonacci Number

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.

# @lc code=start
using LeetCode

function tribonacci_1137(n::Int)::Int
    n <= 1 && return n
    a, b, c = 0, 1, 1
    for _ in 1:(n - 2)
        a, b, c = b, c, a + b + c
    end
    return c
end
# @lc code=end

tribonacci_1137 (generic function with 1 method)

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