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# 70. 爬楼梯

<https://leetcode-cn.com/problems/climbing-stairs/>

## 解法一：dp

由“累加”性质，很容易想到递推方程：`dp[i] = dp[i-1] + dp[i-2]`，dp\[i]表示到达i层的方法总数，由于每次爬一步或两步，因此dp\[i]只有可能由dp\[i-1]和dp\[i-2]而来。

```python
class Solution:
    def climbStairs(self, n: int) -> int:
        if n <= 1:
            return n
        dp = [0] * (n+1)
        dp[1], dp[2] = 1, 2  #初始条件
        for i in range(3, n+1):
            dp[i] = dp[i-1] + dp[i-2]
        return dp[n]
```