ummels

(fn [l u]
  (let [s (apply str (take-while #(<= % u) (iterate #(* % %) l)))
        d (int (Math/ceil (Math/sqrt (count s))))
        n (concat (seq s) (repeat (- (* d d) (count s)) \*))
        m (loop [m {} sx n
                 r (if (even? d) (- d 2) (dec d)) c (- d 1)
                 dr (mapcat #(repeat (* % 2) (if (even? %) -1 1)) (range))
                 dc (mapcat #(repeat (inc (* % 2)) (if (even? %) 1 -1)) (range))]
            (if (empty? sx) m
                (recur (assoc m [r c] (first sx)) (rest sx)

ummels

(fn [s e]
  (let [squares   (apply str (take-while #(<= % e) (iterate #(* % %) s)))
        filler    (drop (count squares) (repeat (#(* % %) (Math/ceil (Math/sqrt (count squares)))) \*))
        elements  (concat squares filler)
        dimension (int (Math/sqrt (count elements)))
        cardinal  (- (* 2 dimension) 1)
        canvas    (vec (repeat cardinal ""))
        start-pos (* 2 (quot (dec dimension) 2))
        path      (take (count elements) (mapcat #(repeat (+ 2 (* 2 %)) (if (odd? %) dec inc)) (range)))
        balance   (fn [c] (#(apply str `(~@% ~@(interpose \  c) ~@%)) (repeat (/ (- cardinal (- (* 2 (count c)) 1)) 2) \ )))]

ummels

;; ummels's solution to Squares Squared
;; https://4clojure.com/problem/138

(fn [start end]
  (letfn
    [(squares [start end]
       (take-while #(<= % end) (iterate #(* % %) start)))
     (arrange [x]
       (let [n (count x)
             dim (int (Math/ceil (Math/sqrt n)))

ummels

;; ummels's solution to Palindromic Numbers
;; https://4clojure.com/problem/150

(fn [n]
  (letfn [(decode [n] (if (< n 10) [n] (conj (decode (quot n 10)) (rem n 10))))
          (encode [x] (reduce #(+ (* % 10) %2) 0 x))
          (next-pal [n]
            (let [N (decode n)
                  l (count N)
                  d (quot l 2)