leecode 1137. 第 N 個泰波那契數

/**
 * Created by zhanghaipeng on 2019/8/12.
 * 泰波那契序列 Tn 定義如下： 
 * T0 = 0, T1 = 1, T2 = 1, 且在 n >= 0 的條件下 Tn+3 = Tn + Tn+1 + Tn+2
 * 給你整數 n，請返回第 n 個泰波那契數 Tn 的值。
 * 來源：力扣（LeetCode
 * 鏈接：https://leetcode-cn.com/problems/n-th-tribonacci-number
 * 著作權歸領釦網絡所有。商業轉載請聯繫官方授權，非商業轉載請註明出處。
 */
public class TribonacciTest {

    public int tribonacci(int n) {
        int[] arr = new int[n+1];
        for (int i = 0 ; i <= n ; i++) {
            if (i == 0 ) {
                arr[i] = 0;
            }else if (i == 1 || i == 2) {
                arr[i] = 1;
            }else {
                arr[i] = arr[i-3] + arr[i-2] + arr[i-1];
            }
        }
        return arr[n];
    }
}