Problem 1: Nothing but the Truth [Elementary]
trueProblem 2: Simple Math [Elementary]
4Problem 3: Intro to Strings [Elementary]
"HELLO WORLD"Problem 4: Intro to Lists [Elementary]
:a :b :cProblem 5: Lists: conj [Elementary]
'(1 2 3 4)Problem 6: Intro to Vectors [Elementary]
:a :b :cProblem 7: Vectors: conj [Elementary]
[1 2 3 4]Problem 8: Intro to Sets [Elementary]
#{:a :b :c :d}Problem 9: Sets: conj [Elementary]
2Problem 10: Intro to Maps [Elementary]
20Problem 11: Maps: conj [Elementary]
[:b 2]Problem 12: Intro to Sequences [Elementary]
3Problem 13: Sequences: rest [Elementary]
[20 30 40]Problem 14: Intro to Functions [Elementary]
8Problem 15: Double Down [Elementary]
#(* 2 %)Problem 16: Hello World [Elementary]
#(str "Hello, " % "!")Problem 17: Sequences: map [Elementary]
'(6 7 8)Problem 18: Sequences: filter [Elementary]
'(6 7)Problem 19: Last Element [Easy]
#(nth % (dec (count %)))Problem 20: Penultimate Element [Easy]
(comp second reverse)Problem 21: Nth Element [Easy]
(fn [coll n] (first (drop n coll)))Problem 22: Count a Sequence [Easy]
#(reduce + (map (constantly 1) %))Problem 23: Reverse a Sequence [Easy]
#(reduce conj () %)Problem 24: Sum It All Up [Easy]
#(reduce + %)Problem 25: Find the odd numbers [Easy]
#(filter odd? %)Problem 26: Fibonacci Sequence [Easy]
#(take % (map first (iterate (fn [[a b]] [b (+ a b)]) [1 1])))Problem 27: Palindrome Detector [Easy]
#(= (seq %) (reverse (seq %)))Problem 28: Flatten a Sequence [Easy]
#(filter (complement sequential?) (rest (tree-seq sequential? seq %)))Problem 29: Get the Caps [Easy]
#(apply str (re-seq #"[A-Z]+" %))Problem 30: Compress a Sequence [Easy]
#(map first (partition-by identity %))Problem 31: Pack a Sequence [Easy]
partition-by identityProblem 32: Duplicate a Sequence [Easy]
mapcat #(list % %)Problem 33: Replicate a Sequence [Easy]
(fn [s n] (mapcat #(repeat n %) s))Problem 34: Implement range [Easy]
#(take (- %2 %1) (iterate inc %1))Problem 35: Local bindings [Elementary]
7Problem 36: Let it Be [Elementary]
[z 1 y 3 x 7]Problem 37: Regular Expressions [Elementary]
"ABC"Problem 38: Maximum value [Easy]
#(last (sort %&))Problem 39: Interleave Two Seqs [Easy]
#(mapcat vector %1 %2)Problem 40: Interpose a Seq [Easy]
(fn [v coll] (butlast (mapcat #(vector % v) coll)))Problem 41: Drop Every Nth Item [Easy]
#(apply concat (partition-all (dec %2) %2 %))Problem 42: Factorial Fun [Easy]
#(apply * (range 1 (inc %)))Problem 43: Reverse Interleave [Medium]
(fn deinterleave [coll n]
(for [i (range n)] (take-nth n (drop i coll))))Problem 44: Rotate Sequence [Medium]
(fn [n coll]
(take (count coll) (drop (mod n (count coll)) (cycle coll))))Problem 45: Intro to Iterate [Easy]
[1 4 7 10 13]Problem 46: Flipping out [Medium]
(fn [f]
(fn [& args] (apply f (reverse args))))Problem 47: Contain Yourself [Easy]
4Problem 48: Intro to some [Easy]
6Problem 49: Split a sequence [Easy]
(fn [n coll]
[(take n coll) (drop n coll)])Problem 50: Split by Type [Medium]
(comp vals (partial group-by type))Problem 51: Advanced Destructuring [Easy]
(range 1 6)Problem 52: Intro to Destructuring [Easy]
[2 4]Problem 53: Longest Increasing Sub-Seq [Hard]
(fn longest-subseq [coll]
(let [take-seq (fn [n pred coll]
(let [hits (count (take-while #(apply pred %) (partition n 1 coll)))]
(take (+ n hits -1) coll)))
chop (fn [coll] (for [n (range (count coll))] (drop n coll)))
parts (chop coll)
seqs (map (partial take-seq 2 #(= (inc %1) %2)) parts)
longest (apply max-key count seqs)]
(if (< (count longest) 2)
[]
longest)))Problem 54: Partition a Sequence [Medium]
(fn p [n c] (when (and (seq c) (>= (count c) n)) (cons (take n c) (p n (drop n c)))))Problem 55: Count Occurrences [Medium]
#(apply merge-with + (for [e %] {e 1}))Problem 56: Find Distinct Items [Medium]
reduce #(if ((set %1) %2) %1 (conj %1 %2)) []Problem 57: Simple Recursion [Elementary]
[5 4 3 2 1]Problem 58: Function Composition [Medium]
(fn [& fs] (reduce (fn [f g] #(f (apply g %&))) fs))Problem 59: Juxtaposition [Medium]
(fn [& fs]
(fn [& as] (map #(apply % as) fs)))Problem 60: Sequence Reductions [Medium]
(fn reduce-
([f coll]
(reduce- f (first coll) (next coll)))
([f init [h & t :as coll]]
(cons init
(lazy-seq
(if (seq coll)
(reduce- f (f init h) t))))))Problem 61: Map Construction [Easy]
#(apply hash-map (interleave %1 %2))Problem 62: Re-implement Iterate [Easy]
(fn iterate- [f init]
(cons init
(lazy-seq
(iterate- f (f init)))))Problem 63: Group a Sequence [Easy]
#(apply merge-with into (for [v %2] {(% v) [v]}))Problem 64: Intro to Reduce [Elementary]
+Problem 65: Black Box Testing [Medium]
(fn [c]
(cond
(= (get (conj c [:t "t"]) :t) "t") :map
(= (get (conj c :t) :t) :t) :set
(= (first (conj (conj c :a) :b)) :b) :list
(= (last (conj (conj c :a) :b)) :b) :vector))Problem 66: Greatest Common Divisor [Easy]
(fn gcd [a b] (if (zero? b) a (recur b (mod a b))))Problem 67: Prime Numbers [Medium]
(fn prime-gen [cnt]
(let [prime? (fn [n]
(not (some #(and
(not= n %)
(zero? (mod n %)))
(range 2 (inc (Math/sqrt n))))))]
(take cnt (filter prime? (iterate inc 2)))))Problem 68: Recurring Theme [Elementary]
[7 6 5 4 3]Problem 69: Merge with a Function [Medium]
(fn [f & ms]
(reduce (fn [m1 m2]
(reduce (fn [m [k v]]
(if (contains? m k)
(update-in m [k] f v)
(assoc m k v)))
m1 m2))
ms))Problem 70: Word Sorting [Medium]
(fn [s]
(sort-by clojure.string/lower-case
(re-seq #"[A-Za-z]+" s)))Problem 71: Rearranging Code: -> [Elementary]
lastProblem 72: Rearranging Code: ->> [Elementary]
reduce +Problem 73: Analyze a Tic-Tac-Toe Board [Hard]
(fn tic-tac-toe [board]
(let [same? (fn [sec] (if (apply = sec) (first sec) nil))
rows (map same? board)
cols (map same? (apply map vector board))
diag1 (same? (map get board (range 3)))
diag2 (same? (map get board (range 2 -1 -1)))]
(some #{:x :o} (concat rows cols [diag1] [diag2]))))Problem 74: Filter Perfect Squares [Medium]
(fn [s]
(let [nums (map #(Integer/parseInt %) (clojure.string/split s #","))
psquare? (fn [n] (let [sqrt (Math/sqrt n)] (= (Math/floor sqrt) sqrt)))
perfect (filter psquare? nums)]
(apply str (interpose "," perfect))))Problem 75: Euler's Totient Function [Medium]
(fn [n]
(if (= n 1)
1
(let [gcd (fn [a b] (if (zero? b) a (recur b (mod a b))))]
(count (filter #{1} (map (partial gcd n) (range 1 n)))))))Problem 76: Intro to Trampoline [Medium]
(range 1 12 2)Problem 77: Anagram Finder [Medium]
(fn [ws]
(set (map (comp set val)
(remove (comp #{1} count val) (group-by frequencies ws)))))Problem 78: Reimplement Trampoline [Medium]
(fn [f & args] (loop [f (apply f args)] (if (fn? f) (recur (f)) f)))Problem 79: Triangle Minimal Path [Hard]
(fn collapse [p] (let [combine (fn [a b] (map + (map #(apply min %) (partition 2 1 a)) b))] (first (reduce combine (reverse p)))))Problem 80: Perfect Numbers [Medium]
(fn [n]
(= n (reduce +
(filter
#(zero? (mod n %))
(range 1 n)))))Problem 81: Set Intersection [Easy]
(fn [a b] (set (filter #(contains? b %) a)))Problem 82: Word Chains [Hard]
(fn find-chain [words]
(let [lev (fn lev [s1 s2]
(cond (empty? s1) (count s2)
(empty? s2) (count s1)
(= (first s1) (first s2)) (lev (rest s1) (rest s2))
:else (inc (min (lev (rest s1) s2)
(lev s1 (rest s2))
(lev (rest s1) (rest s2))))))
neighbors (fn [words word] (filter #(= (lev word %) 1) words))
chain (fn chain [graph visited root]
(let [visited (conj visited root)
neigh (remove visited (graph root))]
(if (= visited words)
true
(some (partial chain graph visited) neigh))))
graph (into {} (for [w words] [w (neighbors words w)]))]
(true? (some (partial chain graph #{}) words))))Problem 83: A Half-Truth [Easy]
not=Problem 84: Transitive Closure [Hard]
(fn [rel]
(let [roots (into {} (for [[k v] (group-by first rel)] [k (mapv second v)]))
children (fn children [rels e]
(let [cs (get rels e [])]
(cons e (mapcat #(children rels %) cs))))]
(set (mapcat #(map vector (repeat %) (rest (children roots %))) (keys roots)))))Problem 85: Power Set [Medium]
(fn powerset [s]
(reduce #(into % (for [subset %] (conj subset %2))) #{#{}} s))Problem 86: Happy numbers [Medium]
(fn happy? [n]
(letfn [(digits [n]
(map #(Integer/parseInt (str %)) (str n)))
(sum-of-squares [n]
(reduce + (map #(* % %) (digits n))))]
(boolean (some #{1} (take 100 (iterate sum-of-squares n))))))Problem 88: Symmetric Difference [Easy]
#(clojure.set/union (clojure.set/difference %1 %2) (clojure.set/difference %2 %1))(fn eulerian [edges]
(let [degrees (fn [edges]
(apply merge-with + {} (for [[a b] edges
:when (not= a b)]
{a 1 b 1})))
gdeg (degrees edges)]
(and
(not (empty? gdeg))
(->> (vals gdeg) (filter odd?) count (>= 2)))))Problem 90: Cartesian Product [Easy]
#(set (for [a (vec %1) b (vec %2)] [a b]))Problem 91: Graph Connectivity [Hard]
(fn fully-connected? [graph]
(let [nodes (set (apply concat graph))
full-graph (set (mapcat (fn [[a b :as n]] [n [b a]]) graph))
children (into {} (for [[k v] (group-by first full-graph)] [k (set (map second v))]))
connections (fn [node]
(->> (iterate #(into % (mapcat children %)) #{node})
(partition 2 1)
(drop-while #(apply not= %))
first first))]
(every? #(= % nodes) (map connections nodes))))Problem 92: Read Roman numerals [Hard]
(fn read-roman [s]
(let [numerals {\M 1000 \D 500 \C 100 \L 50 \X 10 \V 5 \I 1}
nums (partition 2 1 (concat (map numerals s) [0]))]
(reduce (fn [sum [a b]] ((if (< a b) - +) sum a)) 0 nums)))Problem 93: Partially Flatten a Sequence [Medium]
(fn pflatten [tree]
(if (every? sequential? tree)
(mapcat pflatten tree)
[tree]))Problem 94: Game of Life [Hard]
(fn conway [board]
(let [cells (set (for [y (range (count board))
x (range (count (get board y)))
:when (not= \space (get-in board [y x]))]
[x y]))
width (count (first board))
height (count board)
neighbors (fn [[x y]]
(for [dx [-1 0 1] dy (if (zero? dx) [-1 1] [-1 0 1])]
[(+ x dx) (+ y dy)]))
step (fn [cells]
(set (for [[loc n] (frequencies (mapcat neighbors cells))
:when (or (= n 3) (and (= n 2) (cells loc)))]
loc)))
serialize (fn [alive]
(mapv #(apply str %)
(partition width
(for [y (range height) x (range width)
:let [sym (if (alive [x y]) \# \space)]]
sym))))]
(-> cells step serialize)))Problem 95: To Tree, or not to Tree [Easy]
(fn tree? [coll]
(cond
(or (seq? coll) (vector? coll))
(and (= 3 (count coll)) (tree? (nth coll 1)) (tree? (nth coll 2)))
(nil? coll) true
:else false))Problem 96: Beauty is Symmetry [Easy]
#(= ((fn mirror [[n l r :as tree]] (when tree [n (mirror r) (mirror l)])) %) %)Problem 97: Pascal's Triangle [Easy]
(fn [n]
(last (take n (iterate #(map +' `(0 ~@%) `(~@% 0)) [1]))))Problem 98: Equivalence Classes [Medium]
(fn [f coll] (into #{} (map set (vals (group-by f coll)))))Problem 99: Product Digits [Easy]
(fn [a b] (mapv #(Integer/parseInt (str %)) (str (* a b))))Problem 100: Least Common Multiple [Easy]
(fn [& args]
(let [gcd (fn [a b] (if (zero? b) a (recur b (mod a b))))]
(/ (reduce * args) (reduce gcd args))))Problem 101: Levenshtein Distance [Hard]
(memoize
(fn lev [s1 s2]
(cond
(zero? (count s1)) (count s2)
(zero? (count s2)) (count s1)
(= (first s1) (first s2)) (lev (rest s1) (rest s2))
:else (inc (min (lev (rest s1) s2)
(lev s1 (rest s2))
(lev (rest s1) (rest s2)))))))Problem 102: intoCamelCase [Medium]
#(let [words (clojure.string/split % #"-")]
(str (first words)
(apply str (map clojure.string/capitalize (drop 1 words)))))Problem 103: Generating k-combinations [Medium]
(fn combinations [k s]
(cond
(zero? k) #{#{}}
(empty? s) #{}
:else (set (clojure.set/union
(map #(conj % (first s)) (combinations (dec k) (rest s)))
(combinations k (rest s))))))Problem 104: Write Roman Numerals [Medium]
(fn [n]
(let [numerals {"M" 1000 "CM" 900 "D" 500 "CD" 400 "C" 100 "XC" 90
"L" 50 "XL" 40 "X" 10 "IX" 9 "V" 5 "IV" 4 "I" 1}
dec->roman (fn [n]
(loop [n n [[c v] & nums :as all] (reverse (sort-by val numerals)) acc []]
(cond
(zero? n) (apply str acc)
(> v n) (recur n nums acc)
:else (recur (- n v) all (conj acc c)))))]
(dec->roman n)))Problem 105: Identify keys and values [Medium]
(fn kv [acc k [v & vs]]
(cond (nil? v) acc
(keyword? v) (kv (assoc acc v []) v vs)
:e (kv (update-in acc [k] conj v) k vs))) {} *Problem 106: Number Maze [Hard]
(fn find-path [s e]
(loop [opts [s] depth 1]
(if (some #{e} opts)
depth
(letfn [(solutions [n]
(concat
[(* n 2) (+ n 2)]
(if (even? n) [(/ n 2)] [])))]
(recur (mapcat solutions opts) (inc depth))))))Problem 107: Simple closures [Easy]
(fn [n] (fn [b] (int (Math/pow b n))))Problem 108: Lazy Searching [Medium]
(fn lazy-search [& colls]
(if (= 1 (count colls))
(first (first colls))
(let [heads (map first colls) largest (apply max heads)]
(if (apply = heads)
largest
(recur (map (fn [c] (drop-while #(< % largest) c)) colls))))))Problem 110: Sequence of pronunciations [Medium]
#(rest (iterate (fn [coll] (mapcat (juxt count first) (partition-by identity coll))) %))Problem 111: Crossword Puzzle [Hard]
(fn [w p]
(let [sm (map #(replace {\space "" \_ \.} %) p)
co (apply map list sm)
pl (mapcat #(take-nth 2 (partition-by #{\#} %)) (concat sm co))]
(boolean (some #(re-matches (re-pattern (apply str %)) w) pl))))Problem 112: Sequs Horribilis [Medium]
(fn [n s]
(second
((fn sequs [n s]
(loop [cnt 0 acc [] [x & xs] s]
(cond
(or (nil? x) (< n cnt)) [cnt acc]
(coll? x) (let [[c r] (sequs (- n cnt) x)
coll (if (empty? r) acc (conj acc r))]
(recur (+ c cnt) coll xs))
:else (recur (+ x cnt) (if (< n (+ cnt x)) acc (conj acc x)) xs))))
n s)))Problem 113: Making Data Dance [Medium]
#(when %&
(reify
clojure.lang.ISeq
(seq [_] (distinct %&))
(toString [_] (apply str (interpose ", " (sort %&))))))Problem 114: Global take-while [Medium]
(fn gtw [n f [h & t]]
(when-not (or (zero? n) (and (= n 1) (f h)))
(cons h (gtw (if (f h) (dec n) n) f t))))Problem 115: The Balance of N [Medium]
(fn [n]
(let [digits (map #(Integer/parseInt (str %)) (str n))
size (int (/ (count digits) 2))
f (take size digits)
l (take-last size digits)]
(= (reduce + f) (reduce + l))))Problem 116: Prime Sandwich [Medium]
(fn balanced-prime? [n]
(let [factors (cons 2 (iterate (partial + 2) 3))
prime? (fn [n] (not-any? #(zero? (mod n %))
(take-while #(<= % (inc (Math/sqrt n))) factors)))
prime-step (fn [n s] (first (drop-while (complement prime?) (rest (iterate (partial + s) n)))))]
(and (> n 3)
(prime? n)
(= n (/ (+ (prime-step n 2) (prime-step n -2)) 2)))))Problem 117: For Science! [Hard]
(fn cat-n-mouse [grid]
(let [neighbors (fn [[x y]] [[(inc x) y] [(dec x) y] [x (inc y)] [x (dec y)]])
parts (for [y (range (count grid))
x (range (count (nth grid y)))
:let [e (get-in grid [y x])]]
{({\C :cat \M :mouse \# :wall \space :space} e) [x y]})
game (apply merge-with conj {:wall [] :space []} parts)
spaces (conj (set (:space game)) (:mouse game))]
(loop [open [(:cat game)] visited #{}]
(cond
(empty? open) false
(= (first open) (:mouse game)) true
:else (let [visited (conj visited (first open))
neigh (filter spaces (neighbors (first open)))
neigh (remove visited neigh)
open (concat (rest open) (remove visited neigh))]
(recur open visited))))))Problem 118: Re-implement Map [Easy]
(fn map- [f coll]
(lazy-seq
(when-let [s (seq coll)]
(cons (f (first s)) (map- f (rest s))))))Problem 119: Win at Tic-Tac-Toe [Hard]
(fn ttt-win [p b]
(let [win? (fn [board]
(let [same? (fn [sec] (if (apply = sec) (first sec) nil))
rows (map same? board)
cols (map same? (apply map vector board))
diag1 (same? (map get board [0 1 2]))
diag2 (same? (map get board [2 1 0]))]
(some #{:x :o} (concat rows cols [diag1] [diag2]))))
free (for [y (range 3)
x (range 3)
:when (= :e (get-in b [y x]))]
[y x])]
(set (filter #(= p (win? (assoc-in b % p))) free))))Problem 120: Sum of square of digits [Easy]
(fn sum-square [coll]
(let [digits (fn [n] (map #(- (int %) 48) (str n)))
square #(* % %)
sum-digits (fn [n] (reduce + (map square (digits n))))]
(count (filter #(< % (sum-digits %)) coll))))Problem 121: Universal Computation Engine [Medium]
(fn [form]
(fn [values]
(let [env (merge {'+ + '- - '* * '/ /} values)]
((fn eval- [f]
(if (seq? f)
(let [[op & args] f]
(apply (env op) (map eval- args)))
(get env f f)))
form))))Problem 122: Read a binary number [Easy]
#(Integer/parseInt % 2)Problem 124: Analyze Reversi [Hard]
(fn reversi [board p]
(let [o '{b w w b}
d (for [y [-1 0 1] x (if (= 0 y) [-1 1] [-1 0 1])] [y x])
b (into {} (for [y (range 4) x (range 4)] [[y x] (get-in board [y x])]))
e (map key (filter #(= 'e (val %)) b))
wk (fn [st off] (take-while b (rest (iterate #(map + % off) st))))
vl (fn [pth] (let [s (apply str (map b pth)) r (re-pattern (str (o p) "+" p))]
(if (re-seq r s) (take-while #(not= p (b %)) pth))))
mv (fn [st] (set (apply concat (keep vl (map #(wk st %) d)))))]
(into {} (for [st e :let [mvs (mv st)] :when (not-empty mvs)] [st mvs]))))Problem 125: Gus' Quinundrum [Hard]
;; The most common quine
(fn [x] (str x x)) '(fn [x] (str x x))Problem 126: Through the Looking Class [Easy]
ClassProblem 128: Recognize Playing Cards [Easy]
(fn card [[s r]]
(let [suits (zipmap (map str "SHCD") [:spade :heart :club :diamond])
ranks (zipmap (map str (concat (range 2 10) "TJQKA")) (range 13))]
{:suit (suits (str s)) :rank (ranks (str r))}))Problem 131: Sum Some Set Subsets [Medium]
(fn sum-subsets [& s]
(let [ps (fn powerset [s]
(reduce (fn [acc e]
(into acc (map conj acc (repeat e))))
#{#{}}
s))
pss (map #(disj (ps %) #{}) s)
sums (map (fn [p] (set (map #(apply + %) p))) pss)]
(not (empty? (apply clojure.set/intersection sums)))))Problem 132: Insert between two items [Medium]
(fn [c v s]
(mapcat (fn [[a b]] (if (and a b (c a b)) (list a v) (list a)))
(partition-all 2 1 s)))Problem 134: A nil key [Elementary]
(fn [k m]
(if (contains? m k)
(= (m k) nil)
false))Problem 135: Infix Calculator [Easy]
(fn calc [& exp]
(reduce #(if (fn? %1) (%1 %2) (partial %2 %1)) identity exp))Problem 137: Digits and bases [Medium]
(fn to-base [n b]
(loop [n n num ()]
(if (zero? n)
(if (empty? num) '(0) num)
(recur (int (/ n b)) (conj num (mod n b))))))Problem 141: Tricky card games [Medium]
(fn [trump]
(fn [hand]
(let [by-suit (group-by :suit hand)
win-suit (or trump (:suit (first hand)))]
(last (sort-by :rank (win-suit by-suit))))))Problem 143: dot product [Easy]
#(reduce + (map * %1 %2))Problem 144: Oscilrate [Medium]
(fn [x & fs]
(reductions #(%2 %1) x (cycle fs)))Problem 145: For the win [Elementary]
(range 1 40 4)Problem 146: Trees into tables [Easy]
#(into {} (for [[k v] % [k2 v2] v] [[k k2] v2]))Problem 147: Pascal's Trapezoid [Easy]
(fn [row]
(iterate #(map +' `(0 ~@%) `(~@% 0)) row))Problem 148: The Big Divide [Medium]
(fn [n a b]
(let [f #(quot (dec n) %)
g #(/ (*' % (f %) (inc (f %))) 2)]
(- (+ (g a) (g b)) (g (* a b)))))Problem 150: Palindromic Numbers [Medium]
(let [nextp (fn [n]
(let [p #(Long. %)
s (str n)
l (count s)
m (subs s 0 (Math/ceil (/ l 2)))
h (str (inc (p m)))
f (fn [s] (p (str s (subs (clojure.string/reverse s) (if (even? l) 0 1)))))
[a b] (map f [m h])]
(if (>= a n) a b)))]
#(iterate (comp nextp inc) (nextp %)))Problem 153: Pairwise Disjoint Sets [Easy]
(fn [sets]
(= (reduce + (map count sets))
(count (reduce clojure.set/union sets))))Problem 156: Map Defaults [Elementary]
#(apply hash-map (interleave %2 (repeat %1)))Problem 157: Indexing Sequences [Easy]
#(map vector % (range))(fn [f] (fn [& args] (reduce #(apply %1 (vector %2)) f args)))Problem 161: Subset and Superset [Elementary]
#{1 2}Problem 162: Logical falsity and truth [Elementary]
1Problem 164: Language of a DFA [Hard]
(fn run* [dfa]
(let [run1 (fn [[s acc]] (for [[c n] ((:transitions dfa) s)] [n (str acc c)]))
accepted (fn [[s acc]] (when ((:accepts dfa) s) acc))]
(mapcat #(keep accepted %) (take-while not-empty (iterate #(mapcat run1 %) (run1 [(:start dfa) ""]))))))Problem 166: Comparisons [Elementary]
(fn [f a b]
(cond
(f a b) :lt
(f b a) :gt
:else :eq))Problem 168: Infinite Matrix [Medium]
(fn imat
([f] (imat f 0 0))
([f r c] (imat f r c -1 -1))
([f r c h w]
(letfn [(row [st wd]
(lazy-seq
(when-not (zero? wd)
(cons st (row (inc st) (dec wd))))))]
(map #(map (partial f %) (row c w)) (row r h)))))Problem 171: Intervals [Medium]
(fn intervals [s]
(reduce (fn [memo e]
(let [memo (if (empty? memo) [[e e]] memo)
[l h] (nth memo (dec (count memo)))]
(cond
(= e h) memo
(= e (inc h)) (assoc-in memo [(dec (count memo)) 1] e)
:else (conj memo [e e]))))
[] (distinct (sort s))))Problem 173: Intro to Destructuring 2 [Easy]
f vsProblem 177: Balancing Brackets [Medium]
(fn balanced? [s]
(let [p {\( \) \[ \] \{ \}}
a (set "()[]{}")]
(empty?
(reduce (fn [[t & b :as stack] s]
(cond (= (p t) s) b
(a s) (conj stack s)
:else stack))
() s))))(fn [h]
(let [[s r] (apply map list h)
rs (set (map frequencies (partition 5 1 "A23456789TJQKA")))
s? (rs (frequencies r))
f? (apply = s)
g (frequencies (vals (frequencies r)))]
(cond
(and s? f?) :straight-flush
(g 4) :four-of-a-kind
(and (g 2) (g 3)) :full-house
f? :flush
s? :straight
(g 3) :three-of-a-kind
(= 2 (g 2)) :two-pair
(g 2) :pair
:else :high-card)))
problem 43:
#(apply map vector (partition-all %2 %))