# 99 Clojure Problems (19-22)

First off, thanks to all the commenters that have been contributing advice and corrections! It’s definitely helping, and I think I’m making some good progress on my quest.

Here’s another set of simple problems:

```; P19 (**) Rotate a list N places to the left.
(defn rotate [n input]
(let [amount (if (< n 0) (+ n (count input)) n)]
(concat (drop amount input) (slice 0 amount input))))

; P20 (*) Remove the K'th element from a list.
(defn remove_at [k input]
(list
(concat
(slice 0 k input)
(slice (inc k) (count input) input))
(nth input k)))

; P21 (*) Insert an element at a given position into a list.
(defn insert_at [k value input]
(concat
(slice 0  k input)
(list value)
(slice k (count input) input)))

; P22 (*) Create a list containing all integers within a given range.
(comment "clojure already has a (range a b), but it is [a,b), not [a,b]")
(defn s99_range [s e]
(loop [output (list s)
curr (inc s)]
(if (> curr e)
(reverse output)
(recur (cons curr output) (inc curr)))))```

Taking some comments to heart, I came up with an alternate P22. I’m not sure, though whether it’s better or worse than my original. I’m pretty sure that there’s a pretty big difference between the two, but I don’t know enough to say what’s what.

```; P22 (*) Create a list containing all integers within a given range.
; clojure already has a (range a b), but it is [a,b), not [a,b]
(defn s99_range_v [s e]
(loop [output [s]
curr (inc s)]
(if (> curr e)
output
(recur (conj output curr) (inc curr)))))```

The next block may take a while. I’m encountering some real difficulty with P26, but I don’t think I’m ready to start “cheating” and looking for other people’s solutions yet.