【算法题1】上台阶问题

 1 class goUpstairs:
 2     def countWays(self,n):
 3         if n==1:
 4             return 0
 5         if n==2:
 6             return 1
 7         if n==3:
 8             return 2
 9         else:
10             return (self.countWays(n-1)+self.countWays(n-2)) % 1000000007  # 为了防止溢出
11 
12 
13 class goUpstairs2:
14     def countWays(self,n):
15         res=[1,1]
16         if n==1:
17             return 0
18         while len(res)<n:
19             res.append(res[-1]+res[-2])
20         return res[-1] % 1000000007
21 
22 if __name__=="__main__":
23     # for i in range(1,10):
24     #     print(goUpstairs2().countWays(i))
25     for i in range(1, 10):
26         print(goUpstairs().countWays(i))