/
pe8.clj
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/
pe8.clj
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(ns project-euler.pe8
(require [clojure.test :as test]) (:import (clojure.lang LazySeq)))
; Project Euler 8: Largest product in a series
; https://projecteuler.net/problem=8
; The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.
; Find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?
(def thousand-digits
; This is the 1000-digit number from the problem.
"73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450")
(defn string-to-num-seq
"Returns a lazy sequence with only the numbers in string s."
[s]
{:pre [(string? s)]}
(map read-string (re-seq #"[0-9]" s)))
(test/deftest string-to-num-seq-test
(test/is (seq? (string-to-num-seq "123")))
(test/is (instance? LazySeq (string-to-num-seq "123")))
(test/is (= '(1 2 3) (string-to-num-seq "123")))
(test/is (= '(1 2 3) (string-to-num-seq "1a2b3c")))
(test/is (= '() (string-to-num-seq "abc")))
(test/is (thrown? AssertionError (string-to-num-seq nil))))
(defn multiply-seq
"Returns product of all numbers in seq.
Filters out non-number items from input.
Seq with no numbers return 0."
[xs]
{:pre [(seq? xs)]}
(let [nums (filter number? xs)]
(cond
(empty? nums) 0
:else (apply * nums))))
(test/deftest multiply-seq-test
; Test standard usage:
(test/is (number? (multiply-seq '(1 2 3))))
(test/is (= 6 (multiply-seq '(1 2 3))))
(test/is (= -6 (multiply-seq '(-1 2 3))))
(test/is (= 0 (multiply-seq '())))
; Test that non-number items are filtered out:
(test/is (= 6 (multiply-seq '(1 \A 2 "B" 3 :C 'D nil true false))))
; Test pre-conditions:
(test/is (thrown? AssertionError (multiply-seq nil)))
(test/is (thrown? AssertionError (multiply-seq 123)))
(test/is (thrown? AssertionError (multiply-seq "123"))))
(defn solve-pe8
"Returns largest product of n adjacent digits."
[n digits-str]
{:pre [(number? n)
(string? digits-str)]}
(apply max
(map multiply-seq
(partition n 1 (string-to-num-seq digits-str)))))
(test/deftest solve-pe8-test
(test/is (number? (solve-pe8 4 "123456")))
(test/is (= 360 (solve-pe8 4 "123456")))
(test/is (= 5832 (solve-pe8 4 thousand-digits)))
(test/is (= 23514624000 (solve-pe8 13 thousand-digits)))
(test/is (thrown? AssertionError (solve-pe8 "4" "123456")))
(test/is (thrown? AssertionError (solve-pe8 4 123456))))
(defn -main []
(test/run-tests)
(println (solve-pe8 4 "123456"))
(println (solve-pe8 4 thousand-digits))
(println (solve-pe8 13 thousand-digits))
)
(-main)