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

Example 2:

Input: n = 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

 

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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