Solution.kt

fun memo(f: (n: Int) -> Int) : (n: Int) -> Int { 
    val hash = HashMap<Int,Int>()
    return fun (n: Int) : Int {
        if (!hash.contains(n)) { hash[n] = f(n) }
        return hash[n] ?: throw RuntimeException("Souldn't happen")
    }
}

class Solution {
    fun climbStairs(n: Int): Int {
        var search : (n: Int) -> Int = { throw RuntimeException("Shouldn't happen 2") }
        search = memo {
            when (it) {
                1 -> 1
                2 -> 2
                else -> search(it - 1) + search(it - 2)
            }
        }
        
        return search(n)
    }
}