1137. N-th Tribonacci Number

Easy

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.

解題

func tribonacci(n int) int {
    arr := []int{0, 1, 1}

    for i:=3; i<=n; i++ {
        arr = append(arr, arr[i-1] + arr[i-2] + arr[i-3])
    }

    return arr[n]
}