跳台阶问题

def splitnum(n,k,arr)
    if n==0 then
       puts arr.to_s
    end
    for i in k..2
        arr.push(i)
        if n-i>= 0 then
            splitnum(n-i,k,arr)
        end
        arr.pop
    end
end

arr=Array.new()
splitnum(4,1,arr)