4clojure problem solving

14 题以前答案一般没啥区别，略过……

#15

#(* % 2)

adereth’s solution:

* 2

#16

1	format "Hello, %s!"

adereth’s solution:

1	#(str "Hello, " % "!")

#17

'(6 7 8)

adereth’s solution:

[6 7 8]

#18

'(6 7)

adereth’s solution:

'(6 7)

#19

1	#(peek (vec %))

adereth’s solution:

1	(comp first reverse)

#20

1	#(nth (reverse %) 1)

adereth’s solution:

1	(comp second reverse)

#21

(fn getn [ary n]
  (if (= n 0)
    (first ary)
    (getn (rest ary) (dec n))))

adereth’s solution:

1	#(first (drop %2 %1))

#22

1	#(reduce (fn [a b] (inc a)) 0 %)

adereth’s solution:

1	(fn [sequence] (reduce (fn [acc v] (inc acc)) 0 sequence))

#23

1	#(reduce (fn [rs ls] (cons ls rs)) [] %)

adereth’s solution:

(fn [s]
  (loop [result []
         s s]
    (if (seq s)
      (recur (concat [(first s)] result) (rest s))
      result)))

#24

1	#(reduce + %)

adereth’s solution:

apply +

#25

1	#(filter odd? %)

adereth’s solution:

1	filter odd?

#26

1 2	#(take % ((fn fib [a b] (lazy-seq (cons a (fib b (+ b a))))) 1 1))

adereth’s solution:

#(take %
  (map first
    (iterate (fn [[i1 i2]]
      [i2 (+ i1 i2)])
      [1 1])))

#29

1	#(clojure.string/replace % #"[^A-Z]" "")

adereth’s solution:

1	(fn [s] (reduce str (filter #(Character/isUpperCase %) s)))

#27

1	#(= (reverse %) (seq %))

#28

(defn cci [ls r]
  (if (every? sequential? ls)
    (concat r ls)
    (apply cci r (partition-by sequential? ls))))

#(let [f (first %)]
  (if (sequential? f)
    )
  conj [] (first %))

#30

#((fn dis [ss l r]
    (if-let [f (first ss)]
      (let [rss (rest ss)]
      	(if (= l f)
        	(dis rss f r)
        	(dis rss f (conj r f))))
      r)) % nil [])

#((fn dis [ss l r]
    (let [[f & s] ss]
      (cond
        (nil? f) r
        (= l f) (dis s f r)
        :else (dis s f (conj r f))))) % nil [])

adereth’s solution:

1	#(map first (partition-by identity %))

#32

1	#(mapcat (fn [s] [s s]) %)

#34

#((fn rng [s n r]
    (if (< s n)
      (rng (inc s) n (conj r s))
      r)) %1 %2 [])

adereth’s solution:

(fn [start end] (take-while #(< % end)
                            (iterate inc start)
                            )
  )

#35

#37

"ABC"

#38

1	(fn [& s] (reduce (fn mx [a b] (if (> a b) a b)) s))

adereth’s solution:

1 2	(fn [ & xs ] (reduce #(if (> %1 %2) %1 %2) xs))

#39

(fn l [a b & r]
  (if (or (nil? (first a)) (nil? (first b)))
    (flatten r)
    (l (rest a) (rest b) (conj (vec r) (first a) (first b)))))

adereth’s solution:

1 2	(fn [s1 s2] (flatten (map list s1 s2)))

#40

1	(fn [x ys] (butlast (flatten (map #(list % x) ys))))

adereth’s solution:

1	#(butlast (interleave %2 (repeat %1)))

#41

1 2	(fn [ls n] (keep-indexed #(if (> (mod (inc %1) n) 0) %2) ls))

adereth’s solution:

(fn [coll n]
  (->> (partition-all n coll)
       (map (partial take (dec n)))
       (flatten)))

#42

1 2	#((fn factorial [n r] (if (= n 1) r (factorial (dec n) (* n r)))) % 1)

adereth’s solution:

1	#(reduce * (range 1 (inc %)))

#48

#52

[c e]

#57

1	'(5 4 3 2 1)

#62

1	(fn fb ([f b] (lazy-seq (cons b (fb f (f b))))))

aceeca1’s solution:

1	(fn [f x] (reductions #(%2 %1) x (repeat f)))

注：从中学习和理解到：

fn 给命名 name? 后也可以递归；
lazy-seq 适合做无限循环递归的懒序列；
reductions 可以将一个数组通过某个方法做 reduce 结果为一个懒序列；

#64

#66

(fn [a b]
  (let [m (min a b)
        d (fn [a b m]
              (and (= 0 (mod a m))
                   (= 0 (mod b m))))
        r (fn o [a b m] 
               (if (d a b m)
                 m
                 (o a b (dec m))))]
    (r a b m)))

astangl’s solution:

(fn
  [x y]
  (if (= 0 y)
      x
      (recur y (mod x y))))

注：从中学习和理解到：

recur 可以递归 fn 这样的匿名函数；
(mod x y) 当 x < y 时，返回 x ，也就是说 x/y 得 0 余 x；
最大公约数 w 一定也可以除尽 (mod x y) 的余数；

#68

1	'(7 6 5 4 3)

adereth’s solution:

1	[7 6 5 4 3]

#71

last

#72

apply +

adereth’s solution:

1	#(reduce + %)

#81

1	(fn [a b] (reduce #(if (contains? a %2) (conj %1 %2) %1) #{} b))

aceeca1’s solution:

1	(comp set filter)

学到的经验：#{} set 是可以当做 contains 方法来 filter 的。

#99

1	(fn [a b] (map #(Integer/parseInt(str %)) (str (* a b))))

aceeca1’s solution:

1	(comp (partial map #(- (int %) 48)) str *)

学到的经验：可以组合几个方法，或者用 ->> 语法串联方法

#99

#107

1	(fn [n] #(reduce * (repeat n %)))

#134

1	#(= nil (get %2 %1 0))

adereth’s solution:

1	#(nil? (get %2 % true))

#145

1	[1 5 9 13 17 21 25 29 33 37]

#156

1	#(apply merge (map (fn [k] {k %1}) %2))

1	#(apply array-map (mapcat (fn [k] [k %1]) %2))

adereth’s solution:

1	(fn [default values] (reduce #(assoc %1 %2 default) {} values))

#161

#{1 2}

#162

Another solution

Solutions to 4Clojure Easy Problems

#107

1	(fn [n] #(reduce * (repeat n %)))

#134

1	#(= nil (get %2 %1 0))

adereth’s solution:

1	#(nil? (get %2 % true))

#145

1	[1 5 9 13 17 21 25 29 33 37]

#156

1	#(apply merge (map (fn [k] {k %1}) %2))

1	#(apply array-map (mapcat (fn [k] [k %1]) %2))

adereth’s solution:

1	(fn [default values] (reduce #(assoc %1 %2 default) {} values))

#161

#{1 2}

#162

Another solution

Solutions to 4Clojure Easy Problems