## 题目描述

### 英文

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?

Note: Given n will be a positive integer.

Example 1:

``````Input: 2
Output: 2
Explanation: There are two ways to climb to the top.
1. 1 step + 1 step
2. 2 steps``````

Example 2:

``````Input: 3
Output: 3
Explanation: There are three ways to climb to the top.
1. 1 step + 1 step + 1 step
2. 1 step + 2 steps
3. 2 steps + 1 step``````

### 中文

``````输入： 2

1.  1 步 + 1 步
2.  2 步``````

``````输入： 3

1.  1 步 + 1 步 + 1 步
2.  1 步 + 2 步
3.  2 步 + 1 步``````

## 解法一

### Python

``````class Solution(object):
def climbStairs(self, n):
"""
:type n: int
:rtype: int
"""
if n <= 2:
return n
a = 1
b = 2
for i in range(3, n + 1):
c = b
b += a
a = c
return b``````

### Java

``````public class Solution {
public int climbStairs(int n) {
if (n <= 2) {
return n;
}
int a = 1;
int b = 2;
for (int i = 3; i <= n; i++) {
int c = b;
b += a;
a = c;
}
return b;
}
}``````

### C++

``````class Solution {
public:
int climbStairs(int n) {
if (n <= 2) {
return n;
}
int a = 1;
int b = 2;
for (int i = 3; i <= n; i++) {
int c = b;
b += a;
a = c;
}
return b;
}
};``````