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murdho's solution

to Armstrong Numbers in the Clojure Track

Published at Jul 13 2018 · 0 comments
Test suite


This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

An Armstrong number is a number that is the sum of its own digits each raised to the power of the number of digits.

For example:

  • 9 is an Armstrong number, because 9 = 9^1 = 9
  • 10 is not an Armstrong number, because 10 != 1^2 + 0^2 = 1
  • 153 is an Armstrong number, because: 153 = 1^3 + 5^3 + 3^3 = 1 + 125 + 27 = 153
  • 154 is not an Armstrong number, because: 154 != 1^3 + 5^3 + 4^3 = 1 + 125 + 64 = 190

Write some code to determine whether a number is an Armstrong number.


Wikipedia https://en.wikipedia.org/wiki/Narcissistic_number

Submitting Incomplete Solutions

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(ns armstrong-numbers-test
  (:require [clojure.test :refer [deftest is testing]]
            [armstrong-numbers :refer [armstrong?]]))

(deftest armstrong-number-5
  (testing "Single digit numbers are Armstrong numbers"
    (is (armstrong? 5))))

(deftest not-armstrong-number-10
  (testing "There are no 2 digit Armstrong numbers"
    (is (not (armstrong? 10)))))

(deftest armstrong-number-153
  (testing "Three digit number that is an Armstrong number"
    (is (armstrong? 153))))

(deftest not-armstrong-number-100
  (testing "Three digit number that is not an Armstrong number"
    (is (not (armstrong? 100)))))

(deftest armstrong-number-9474
  (testing "Four digit number that is an Armstrong number"
    (is (armstrong? 9474))))

(deftest not-armstrong-number-9475
  (testing "Four digit number that is not an Armstrong number"
    (is (not (armstrong? 9476)))))

(deftest armstrong-number-9926315
  (testing "Seven digit number that is an Armstrong number"
    (is (armstrong? 9926315))))

(deftest not-armstrong-number-9926314
  (testing "Seven digit number that is not an Armstrong number"
    (is (not (armstrong? 9926314)))))
(ns armstrong-numbers
  (:require [clojure.string :as s]))

(defn digits [n]
  (map #(Integer/parseInt %)
      (-> n
        (s/split #""))))

(defn reverse-pow [n m]
  (int (Math/pow m n)))

(defn digits-to-power-of-length [n]
  (let [d (digits n)
        l (count d)
        f (partial reverse-pow l)]
    (map f d)))

(defn armstrong? [n]
  (= n (reduce + (digits-to-power-of-length n))))

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