Description (leetcode)

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

submission

impl Solution {
    // fibnacci sequence, we can demonstrate this by dp
    // with transform: dp[i] = dp[i - 1] + dp[i - 2]
    pub fn climb_stairs(n: i32) -> i32 {
         (0..n)
            .fold((1, 0), |(res, prev), _| (res + prev, res))
            .0
    }
}