leetcode——1137.第N个斐波那契数

 1 class Solution:
 2     def tribonacci(self, n: int) -> int:
 3         if n<1:
 4             return n
 5         if n==2:
 6             return 1
 7         a=[0,1,1]
 8         m=0
 9         t=1
10         s=2
11         while s<=n-1:
12             a.append(a[m]+a[t]+a[s])
13             m,t,s=t,s,s+1
14         return a[-1]