1137. N-th Tribonacci Number(Memory Usage: 13.9 MB, less than 100.00% of Python3)

其实思路很简单，套用一下普通斐波那契数列的非递归做法即可，不过这个成绩我一定要纪念一下，哈哈哈哈哈

代码在这儿：

class Solution:
def tribonacci(self, n: int) -> int:
a, b, c =0, 1, 1
if n is 0:
return 0
if n is 1:
return 1
if n is 2:
return 1
for i in range(2, n):
a, b ,c = b, c, a+b+c
return c