1137. N-th Tribonacci Number

⭐

題目敘述

The Tribonacci sequence Tn is defined as follows:

T0 = 0, T1 = 1, T2 = 1, and T~~n+3~~ = Tn + T~~n+1~~ + T~~n+2~~ for n >= 0.

Given n, return the value of Tn.

Example 1

Input: n = 4 Output: 4 Explanation: T3 = 0 + 1 + 1 = 2 T4 = 1 + 1 + 2 = 4

Example 2

Input: n = 25 Output: 1389537

解題思路

Solution

class Solution {
    public int tribonacci(int n) {
        int[] Tn = new int[] {0, 1, 1, 0};

        switch(n){
            case 0:
                return Tn[0];
            case 1:
                return Tn[1];
            case 2: 
                return Tn[2];
        }

        for(int i = 3; i <= n; i++){
            Tn[3] = Tn[2] + Tn[1] + Tn[0];
            Tn[0] = Tn[1];
            Tn[1] = Tn[2];
            Tn[2] = Tn[3];
        }

        return Tn[3];
    }
}