class Solution {
func climbStairs(_ n: Int) -> Int {
if n <= 2 {
return n
}
var arr: [Int] = Array(repeating: 0, count: n+1)
arr[0] = 1
arr[1] = 1
for i in 2...n {
arr[i] = arr[i-2] + arr[i-1]
}
return arr[n]
}
}