4clj #150 (palindrome)

p150.clj

(def g
  (letfn [(ng-next [n]
            (let [s           (str n)
                  seg2-right  (.length s)
                  seg1-right  (quot seg2-right 2)
                  seg1        (.substring s 0 seg1-right)]
              (if (= "" (.replaceAll s "9" ""))
                (+ 2 n)
                (if (even? seg2-right)
                  (let [seg1-ng (str (inc (Long/valueOf seg1)))]
                    (Long/valueOf (str seg1-ng (clojure.string/reverse seg1-ng))))
                  (let [seg1-ng (str (inc (Long/valueOf (str seg1 (.substring s seg1-right (inc seg1-right))))))
                        seg2-ng (clojure.string/reverse (.substring seg1-ng 0 seg1-right))]
                    (Long/valueOf (str seg1-ng seg2-ng)))))))
          (ng-norm [n] (let [s           (str n)
                             seg2-right  (.length s)
                             s-even?     (even? seg2-right)
                             seg1-right  (quot seg2-right 2)
                             seg2-left   (+ seg1-right (if s-even? 0 1))
                             seg1        (.substring s 0 seg1-right)
                             cmp         (.compareTo seg1 (clojure.string/reverse (.substring s seg2-left seg2-right)))]
                         (cond (zero? cmp) n
                               (pos?  cmp) (Long/valueOf (str seg1 (.substring s seg1-right seg2-left) (clojure.string/reverse seg1)))
                               :else       (if s-even?
                                             (let [seg1-ng (str (inc (Long/valueOf seg1)))]
                                               (Long/valueOf (str seg1-ng (clojure.string/reverse seg1-ng))))
                                             (let [seg1-ng (str (inc (Long/valueOf (str seg1 (.substring s seg1-right seg2-left)))))
                                                   seg2-ng (clojure.string/reverse (.substring seg1-ng 0 seg1-right))]
                                               (Long/valueOf (str seg1-ng seg2-ng)))))))]
    (fn [n] (if (< n 10)
             (concat (range n 10) (iterate ng-next 11))
             (iterate ng-next (ng-norm n))))))