I have two problems with the following code.
First, I have this `tos' business (to-string) because:
user=> (first "abc")
\a
user=> (rest "abc")
(\b \c)
Since I wanted to get strings out of strings, a character or a
collection is no good.
Second, I ended-up having to use a mutable atom `res' because I
couldn't figure out how to do it otherwise.
Any pointer on how to tackle either or both problems welcome.
(ns word-play)
(defn rotate
"Take a collection and left rotates it n steps.
If n is negative, the collection is rotated right.
Executes in O(n) time."
([coll]
(rotate 1 coll))
([n coll]
(let [c (count coll)]
(take c (drop (mod n c) (cycle coll))))))
(defn all-rotations [word]
"all rots"
(take (count (str word)) (cycle (iterate rotate (str word)))))
(defn anagram [word]
"To generate all anagrams of a given string of length n, the most
obvious solution is to consider all n rotations of the string one
by one, and for each such rotation, concatenate its first character
with each of the anagrams of the new string composed of all but its
first character."
(cond
(= (count word) 0) '("")
(= (count word) 1) (list word)
true
(let [all (all-rotations word)
tos #(str (reduce str %))
wst (map tos all)
res (atom "")]
(doseq [w wst]
(let [s (str w)
f (str (first (str s)))
n (str (tos (next (str s))))
j #(str f (tos %))
a (ana3 n)
r (map j a)]
(swap! res concat r)))
@res)))
user=> (anagram "1")
("1")
user=> (anagram "12")
("12" "21")
user=> (anagram "123")
("123" "132" "231" "213" "312" "321")
user=> (anagram "lisp")
("lisp" "lips" "lspi" "lsip" "lpis" "lpsi" "ispl" "islp" "ipls" "ipsl"
"ilsp" "ilps" "spli" "spil" "slip" "slpi" "sipl" "silp" "plis" "plsi"
"pisl" "pils" "psli" "psil")
user=>
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