Hindol's solution to Armstrong Numbers on the Clojure track

Instructions

Test suite

Solution

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.

Source

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

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

armstrong_numbers_test.clj

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

(deftest armstrong-number-0
  (testing "Zero is an Armstrong number"
    (is (armstrong? 0))))

(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? 9475)))))

(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)))))

(deftest armstrong-number-21897142587612075
  (testing "Seventeen digit number that is an Armstrong number"
    (is (armstrong? 21897142587612075))))

project.clj

(defproject armstrong-numbers "0.1.0-SNAPSHOT"
  :description "armstrong-numbers exercise"
  :url "https://github.com/exercism/clojure/tree/master/exercises/armstrong-numbers"
  :dependencies [[org.clojure/clojure "1.9.0"]
                 [org.clojure/math.numeric-tower "0.0.4"]])

src/armstrong_numbers.clj

(ns armstrong-numbers
  (:require [clojure.math.numeric-tower :as math]))


(defn armstrong? [num]
  (->> num
       (str)
       (map int)
       (map #(- % (int \0)))
       (map #(math/expt % (count (str num))))
       (reduce +)
       (= num)))

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Hindol's solution

to Armstrong Numbers in the Clojure Track