# 爬楼梯

有一楼梯共M级，刚开始时你在第一级，若每次只能跨上一级或二级，要走上第M级，共有多少种走法？

**分析**： 这个问题要倒过来看，要到达n级楼梯，只有两种方式，从（n-1）级 或 （n-2）级到达的。所以可以用递推的思想去想这题，假设有一个数组s\[n], 那么s\[1] = 1（由于一开始就在第一级，只有一种方法）， s\[2] = 1（只能从s\[1]上去 没有其他方法）。

那么就可以推出s\[3] \~ s\[n]了。

下面继续模拟一下， s\[3] = s\[1] + s\[2]， 因为只能从第一级跨两步， 或者第二级跨一步。

```
function cStairs(n) {
    if(n === 1 || n === 2) {
        return 1;
    } else {
        return cStairs(n-1) + cStairs(n-2)
    }
}
复制代码
```

嗯嗯，没错呢，其实就是斐波纳契数列没跑了


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