Climbing Stairs

You are climbing a stair case. It takes n steps to reach to the top.

Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

分析： 

题目比较简单，小的细节没有把握好。

class Solution {
public:
    int climbStairs(int n) { 
        if(n==1) return 1;
    
        int all[n+1];
        all[0] = 1;
        all[1] = 1;
        
        for(int i=2;i<=n;i++){
            all[i] = all[i-1] + all[i-2];
        }
        
        return all[n];
    }
};

python

class Solution:
    # @param n, an integer
    # @return an integer
    def climbStairs(self, n):
        if n==1:
            return 1
            
        all = [0]*(n+1)
        all[1] = 1
        all[2] = 2
        for i in range(3,n+1):
            all[i] = all[i-1] + all[i-2]
        
        return all[n]
        

总结：

1. 又忘了判断n,  注意任何一个输入的变量都要先想一想

2.  这是fabonacci 数列，其实只要保存两个值就可以了。  因为 fabonacci 数列有通项公式，所有可以用 log(n+1) 的复杂度解出来