70. 爬楼梯

70. 爬楼梯

假设你正在爬楼梯。需要 n 阶你才能到达楼顶。

每次你可以爬 1 或 2 个台阶。你有多少种不同的方法可以爬到楼顶呢？

注意：给定 n 是一个正整数。

示例 1：

输入： 2
输出： 2

解释： 有两种方法可以爬到楼顶。
1.  1 阶 + 1 阶
2.  2 阶

 

 c++

class Solution {
public:
    int climbStairs(int n) {
        int p = 0, q = 0, r = 1;
        for (int i = 1; i <= n; ++i) {
            p = q; 
            q = r; 
            r = p + q;
        }
        return r;
    }
};

 

class Solution{
public:
    int climbStairs(int n){
        int p=0,q=0,r=1;
        for(int i =1,i<=n; ++i){
            p = q;
            q =r;
            r = p+q;
        }
        return r;
    }
};

java

class Solution:
    def climbStairs(self, n: int) -> int:
        if n<=2:return n
        f_1, f_2 = 1, 2
        f = 0
        for i in range(2, n):
            f = f_1 + f_2
            f_1 = f_2  
            f_2 = f
        
        return f

 Python

class Solution:
    def climbStairs(self, n: int) -> int:
        if n<=2:return n
        f_1, f_2 = 1, 2
        f = 0
        for i in range(2, n):
            f = f_1 + f_2
            f_1 = f_2  
            f_2 = f
        
        return f

class Solution:
    def climbStairs(self,n: int) -> int:
        if n<=2: return n
        f_1, f_2 =1,2
        f =0
        for i in range(2,n):
            f = f_1 +f_2
            f_1 =f_2
            f_2 = f
        return f

 

class Solution:
    def climbStairs(self,n: int) -> int:
        if n<=2: return n
        f_1 ,f_2 = 1,2
        f =0
        for i in range(2,n):
            f =f_1 +f_2
            f_1 =f_2
            f_2 = f
        return f