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
answer <= 2^31 - 1
.struct Solution;
impl Solution {
fn tribonacci(n: i32) -> i32 {
let n = n as usize;
let mut a: Vec<i32> = vec![0; 38];
a[0] = 0;
a[1] = 1;
a[2] = 1;
for i in 3..=n {
a[i] = a[i - 1] + a[i - 2] + a[i - 3];
}
a[n]
}
}
#[test]
fn test() {
assert_eq!(Solution::tribonacci(25), 1_389_537);
}