## 70. Climbing Stairs

You are climbing a staircase. It takes `n`

steps to reach the top.

Each time you can either climb `1`

or `2`

steps. In how many distinct ways can you climb to the top?

**Example 1:**

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

**Example 2:**

Input:n = 3Output:3Explanation: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

**Constraints:**

`1 <= n <= 45`

## Rust Solution

```
struct Solution;
impl Solution {
fn climb_stairs(n: i32) -> i32 {
match n {
1 | 2 => n,
k => (2..k).fold((1, 2), |acc, _| (acc.1, acc.0 + acc.1)).1,
}
}
}
#[test]
fn test() {
assert_eq!(Solution::climb_stairs(3), 3);
assert_eq!(Solution::climb_stairs(2), 2);
assert_eq!(Solution::climb_stairs(1), 1);
}
```

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