string - Clojure 中惯用的字符串旋转

Question

如何在 Clojure 中以惯用方式为 Burrows-Wheeler transform 旋转字符串？

我想到了这个，它使用了 (cycle "string")，但感觉有点势在必行:

(let [s (str "^" "banana" "|")
      l (count s)
      c (cycle s)
      m (map #(take l (drop % c)) (range l))]
  (apply map str m))
=> ("^banana|" "banana|^" "anana|^b" "nana|^ba" "ana|^ban" "na|^bana" "a|^banan" "|^banana")

我不确定这是否符合代码高尔夫的条件。有没有更简洁的方法来做到这一点？

Answer 1

我会这样做:

(defn bwrot [s]
  (let [s (str "^" s "|")]
    (for [i (range (count s))]
      (str (subs s i) (subs s 0 i)))))

或:

(defn bwrot [s]
  (let [n (+ 2 (count s))
        s (str "^" s "|^" s "|")]
    (for [i (range n)]
      (subs s i (+ i n)))))

第二个应该分配更少(每次迭代一个字符串而不是三个)。