1137. 第 N 个泰波那契数

class Solution {
   public int tribonacci(int n) {
          int T0 = 0;
          int T1 = 1;
          int T2 = 1;
          int arr[] = new int [40];
          arr[0] = 0;
          arr[1] = 1;
          arr[2] = 1;
          for(int i = 3 ; i <= n ; i++) {
              arr[i] = arr[i-2]+ arr[i-1]+arr[i-3];
          }
          return arr[n];    
        }
    }

有一种更省空间 不用开一个array

class Solution {
    public int tribonacci(int n) {
        if (n==0)
            return 0;
        int T1 = 0;
        int T2 = 1;
        int T3 = 1;
        for (int i = 4; i <= n+1; i++) {
            int T4 = T1 + T2 + T3;
            T1 = T2;
            T2 = T3;
            T3 = T4;
        }
        return T3;
    }
}