My 4Clojure Solutions(1 to 50)
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1. Nothing but the Truth
(= true true)
2. Simple Math
(= (- 10 (* 2 3)) 4)
3. Intro to Strings
(= "HELLO WORLD" (.toUpperCase "hello world"))
4. Intro to Lists
(= (list :a :b :c) '(:a :b :c))
5. Lists: conj
(= '(1 2 3 4) (conj '(2 3 4) 1))
(= '(1 2 3 4) (conj '(3 4) 2 1))
6. Intro to Vectors
(= [:a :b :c] (list :a :b :c) (vec '(:a :b :c)) (vector :a :b :c))
7. Vectors: conj
(= [1 2 3 4] (conj [1 2 3] 4))
(= [1 2 3 4] (conj [1 2] 3 4))
8. Intro to Sets
(= #{:a :b :c :d} (set '(:a :a :b :c :c :c :c :d :d)))
(= #{:a :b :c :d} (clojure.set/union #{:a :b :c} #{:b :c :d}))
9. Sets: conj
(= #{1 2 3 4} (conj #{1 4 3} 2))
10. Intro to Maps
(= 20 ((hash-map :a 10, :b 20, :c 30) :b))
(= 20 (:b {:a 10, :b 20, :c 30}))
11. Maps: conj
(= {:a 1, :b 2, :c 3} (conj {:a 1} [:b 2] [:c 3]))
12. Intro to Sequences
(= 3 (first '(3 2 1)))
(= 3 (second [2 3 4]))
(= 3 (last (list 1 2 3)))
13. Sequences: rest
(= [20 30 40] (rest [10 20 30 40]))
14. Intro to Functions
(= 8 ((fn add-five [x] (+ x 5)) 3))
(= 8 ((fn [x] (+ x 5)) 3))
(= 8 (#(+ % 5) 3))
(= 8 ((partial + 5) 3))
15. Double Down
(defn double-down [x]
(* x 2))
(= (double-down 3) 6)
16. Hello World
(= (#(str "Hello, " % "!") "Dave")
"Hello, Dave!")
17. Sequences: map
(= '(6 7 8) (map #(+ % 5) '(1 2 3)))
18. Sequences: filter
(= '(6 7) (filter #(> % 5) '(3 4 5 6 7)))
19. Last Element
(= (-> [1 2 3 4 5]
reverse
first) 5)
(defn last-elem [[head & tail]]
(if (seq tail)
(recur tail)
head))
(= (last-elem [1 2 3 4 5]) 5)
20. Penultimate Element
(= (-> '(1 2 3 4 5)
reverse
rest
first) 4)
(defmulti penultimate
(fn [input]
(= (count input) 1)))
(defmethod penultimate true [input] nil)
(defmethod penultimate false [[head after_head & tail :as input]]
(if (seq tail)
(recur (rest input))
head))
(println (= (penultimate '(1 2 3 4 5)) 4))
(println (= (penultimate '(1)) nil))
(println (= (penultimate '()) nil))
21. Nth Element
(defn my-nth [input_seq n]
{:pre [(>= n 0)]}
(loop [counter 0
input input_seq]
(if (= counter n)
(first input)
(recur (inc counter) (rest input)))))
(println (= (my-nth '(4 5 6 7) 2) 6))
(my-nth '(4 5 6 7) -1)
(= (#(->> %1
(drop %2)
first) '(4 5 6 7) 2) 6)
22. Count a Sequence
(defn my-count [input_seq]
(apply +
(for [elem input_seq] 1)))
(println (= (my-count '(1 2 3 3 1)) 5))
(println (= (my-count "Hello World") 11))
23. Reverse a Sequence
(= (#(into '() %) [1 2 3 4 5])
[5 4 3 2 1])
24. Sum It All Up
(= (#(apply + %) [1 2 3]) 6)
25. Find the odd numbers
(= (#(filter odd? %) [4 2 1 6]) '(1))
26. Fibonacci Sequence
(defn fib [n]
(->> (iterate (fn [[a b]] [b (+ a b)]) [1 1])
(map first)
(take n)))
(= (fib 8) '(1 1 2 3 5 8 13 21))
27. Palindrome Detector
(defn palindrome? [[head & tail :as input_seq]]
(cond
(= (count input_seq) 1) true
(empty? input_seq) true
:else (and (= head (last tail)) (recur (butlast tail)))))
(true? (palindrome? "racecar"))
28. Flatten a Sequence
(defn- my-flatten-helper [[head & tail :as input_seq] result]
(cond
(empty? input_seq) result
(sequential? head) (recur tail (concat (my-flatten-helper head '()) result))
:else (recur tail (conj result head))))
(defn my-flatten [input-seq]
(reverse (my-flatten-helper input-seq '())))
(println (= (my-flatten '((1 2) 3 [4 [5 6]])) '(1 2 3 4 5 6)))
(println (= (my-flatten ["a" ["b"] "c"]) '("a" "b" "c")))
(println (= (my-flatten '((((:a))))) '(:a)))
29. Get the Caps
(defn is-upper? [input_char]
(contains?
(set "ABCDEFGHIJKLMNOPQRSTUVWXYZ")
input_char))
(defn get-caps [input_string]
(apply str (filter is-upper? input_string)))
(println (= (get-caps "HeLlO, WoRlD!") "HLOWRD"))
(println (empty? (get-caps "nothing")))
(println (= (get-caps "$#A(*&987Zf") "AZ"))
30. Compress a Sequence
(defn compress [input_seq]
(loop [[head & tail :as input] input_seq
result '()]
(cond
(empty? input) (reverse result)
(= head (first result)) (recur tail result)
:else (recur tail (cons head result)))))
(= (apply str (compress "Leeeeeerrroyyy")) "Leroy")
31. Pack a Sequence
(defn pack [input_seq]
(loop [[head & tail :as input] input_seq
[result_head & result_tail :as result] '()]
(cond
(empty? input) (reverse result)
(= head (first result_head)) (recur tail (cons (cons head result_head) result_tail))
:else (recur tail (cons (list head) result)))))
(= (pack [1 1 2 1 1 1 3 3]) '((1 1) (2) (1 1 1) (3 3)))
32. Duplicate a Sequence
(defn duplicate [input_seq]
(loop [[head & tail :as input] input_seq
result '()]
(if (empty? input)
(reverse result)
(recur tail (conj result head head)))))
(= (duplicate [1 2 3]) '(1 1 2 2 3 3))
33. Replicate a Sequence
(defn replicate [input_seq n]
(loop [[head & tail :as input] input_seq
result '()]
(if (empty? input)
(reverse result)
(recur tail (concat (repeat n head) result)))))
(= (replicate [1 2 3] 2) '(1 1 2 2 3 3))
34. Implement range
(defn my-range [start end]
(loop [counter start
result '()]
(if (= counter end)
(reverse result)
(recur (inc counter) (conj result counter)))))
(= (my-range 1 4) '(1 2 3))
35. Local bindings
(= 7 (let [x 5] (+ 2 x)))
(= 7 (let [x 3, y 10] (- y x)))
(= 7 (let [x 21] (let [y 3] (/ x y))))
36. Let it Be
(println (= 10 (let [x 7 y 3 z 1] (+ x y))))
(println (= 4 (let [x 7 y 3 z 1] (+ y z))))
(println (= 1 (let [x 7 y 3 z 1] z)))
37. Regular Expressions
(= "ABC" (apply str (re-seq #"[A-Z]+" "bA1B3Ce ")))
38. Maximum value
(defn my-max [& args]
(loop [[head & tail :as input] args
result head]
(cond
(empty? input) result
(> head result) (recur tail head)
:else (recur tail result))))
(= (my-max 45 67 11) 67)
39. Interleave Two Seqs
(defn my-interleave [seq1 seq2]
(loop [[head1 & tail1 :as s1] seq1
[head2 & tail2 :as s2] seq2
result '()]
(cond
(or (empty? s1) (empty? s2)) (reverse result)
:else (recur tail1 tail2 (conj result head1 head2)))))
(= (my-interleave [1 2 3] [:a :b :c]) '(1 :a 2 :b 3 :c))
40. Interpose a Seq
(defn my-interpose [elem input_seq]
(loop [[head & tail :as input] input_seq
result '()]
(if (empty? input)
(butlast (reverse result))
(recur tail (conj result head elem)))))
(= (my-interpose :z [:a :b :c :d]) [:a :z :b :z :c :z :d])
41. Drop Every Nth Item
(defn drop-nth [input_seq n]
(loop [[head & tail :as input] input_seq
counter 1
result '()]
(cond
(empty? input) (reverse result)
(= counter n) (recur tail 1 result)
:else (recur tail (inc counter) (conj result head)))))
(= (drop-nth [1 2 3 4 5 6] 4) [1 2 3 5 6])
42. Factorial Fun
(def factorial (memoize (fn [n]
{:pre [(>= n 0)]}
(condp = n
0 1
(* n (factorial (dec n)))))))
(= (factorial 8) 40320)
43. Reverse Interleave
(defn reverse-interleave [input_seq n]
(loop [input input_seq
result (vec (repeat n []))
counter 0]
(match [input counter]
[([] :seq) _] result
[_ n] (recur input result 0)
[([head & tail] :seq) counter] (recur tail
(update-in result [counter] #(conj % head))
(inc counter)))))
(println (= (reverse-interleave [1 2 3 4 5 6] 2) '((1 3 5) (2 4 6))))
(println (= (reverse-interleave (range 9) 3) '((0 3 6) (1 4 7) (2 5 8))))
(println (= (reverse-interleave (range 10) 5) '((0 5) (1 6) (2 7) (3 8) (4 9))))
44. Rotate Sequence
(defn- rotate-left [n input_seq]
{:pre [(>= n 0)]}
(loop [result input_seq
counter (mod n (count input_seq))]
(let [head (first result)
tail (vec (rest result))]
(if (= counter 0)
result
(recur (conj tail head) (dec counter))))))
(defn- rotate-right [n input_seq]
{:pre [(>= n 0)]}
(->> input_seq
(reverse)
(rotate-left n)
(reverse)))
(defn rotate [n input_seq]
(cond
(= n 0) input_seq
(> n 0) (rotate-left n input_seq)
(< n 0) (rotate-right (* -1 n) input_seq)))
(println (= (rotate 2 [1 2 3 4 5]) '(3 4 5 1 2)))
(println (= (rotate -2 [1 2 3 4 5]) '(4 5 1 2 3)))
(println (= (rotate 6 [1 2 3 4 5]) '(2 3 4 5 1)))
(println (= (rotate 1 '(:a :b :c)) '(:b :c :a)))
(println (= (rotate -4 '(:a :b :c)) '(:c :a :b)))
45. Intro to Iterate
(= [1 4 7 10 13] (take 5 (iterate #(+ 3 %) 1)))
46. Flipping out
(defn flip [f]
(fn [& args]
(apply f (reverse args))))
(= [1 2 3] ((flip take) [1 2 3 4 5] 3))
47. Contain Yourself
(println (contains? #{4 5 6} 4))
(println (contains? [1 1 1 1 1] 4))
(println (contains? {4 :a 2 :b} 4))
(println (not (contains? [1 2 4] 4)))
48. Intro to some
(println (= 6 (some #{2 7 6} [5 6 7 8])))
(println (= 6 (some #(when (even? %) %) [5 6 7 8])))
49. Split a sequence
(defn my-split [n input_seq]
[(subvec input_seq 0 n) (subvec input_seq n)])
(println (= (my-split 3 [1 2 3 4 5 6]) [[1 2 3] [4 5 6]]))
(println (= (my-split 1 [:a :b :c :d]) [[:a] [:b :c :d]]))
(println (= (my-split 2 [[1 2] [3 4] [5 6]]) [[[1 2] [3 4]] [[5 6]]]))
50. Split by Type
(defn- split-by-type-helper [t input_seq]
(filterv #(instance? t %) input_seq))
(defn split-by-type [input_seq]
(let [types (set (map type input_seq))]
(set (for [t types]
(split-by-type-helper t input_seq)))))