1137. 第 N 个泰波那契数

 1 class Solution(object):
 2     def tribonacci(self, n):
 3         """
 4         :type n: int
 5         :rtype: int
 6         """
 7         if n==0:
 8             return 0
 9         if n<3:
10             return 1
11         f=[0 for i in range(n+1)]
12         f[0]=0
13         f[1]=1
14         f[2]=1
15         for i in range(3,n+1):
16             f[i]=f[i-1]+f[i-2]+f[i-3]
17         return f[-1]