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to Phone Number in the Clojure Track

Published at Jul 13 2018 · 0 comments
Test suite

Clean up user-entered phone numbers so that they can be sent SMS messages.

The North American Numbering Plan (NANP) is a telephone numbering system used by many countries in North America like the United States, Canada or Bermuda. All NANP-countries share the same international country code: 1.

NANP numbers are ten-digit numbers consisting of a three-digit Numbering Plan Area code, commonly known as area code, followed by a seven-digit local number. The first three digits of the local number represent the exchange code, followed by the unique four-digit number which is the subscriber number.

The format is usually represented as


where N is any digit from 2 through 9 and X is any digit from 0 through 9.

Your task is to clean up differently formatted telephone numbers by removing punctuation and the country code (1) if present.

For example, the inputs

  • +1 (613)-995-0253
  • 613-995-0253
  • 1 613 995 0253
  • 613.995.0253

should all produce the output


Note: As this exercise only deals with telephone numbers used in NANP-countries, only 1 is considered a valid country code.


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(ns phone-number-test
  (:require [clojure.test :refer [deftest is]]

(deftest cleans-number
  (is (= "1234567890" (phone-number/number "(123) 456-7890"))))

(deftest cleans-number-with-dots
  (is (= "5558675309" (phone-number/number "555.867.5309"))))

(deftest valid-when-11-digits-and-first-is-1
  (is (= "9876543210" (phone-number/number "19876543210"))))

(deftest invalid-when-11-digits
  (is (= "0000000000" (phone-number/number "21234567890"))))

(deftest invalid-when-9-digits
  (is (= "0000000000" (phone-number/number "123456789"))))

(deftest area-code
  (is (= "123" (phone-number/area-code "1234567890"))))

(deftest area-code-with-dots
  (is (= "555" (phone-number/area-code "555.867.5309"))))

(deftest area-code-with-parentheses
  (is (= "987" (phone-number/area-code "(987) 654-3210"))))

(deftest area-code-with-full-us-phone-number
  (is (= "123" (phone-number/area-code "11234567890"))))

(deftest pretty-print
  (is (= "(123) 456-7890" (phone-number/pretty-print "1234567890"))))

(deftest pretty-print-with-dots
  (is (= "(555) 867-5309" (phone-number/pretty-print "555.867.5309"))))

(deftest pretty-print-with-full-us-phone-number
  (is (= "(987) 654-3210" (phone-number/pretty-print "19876543210"))))
(ns phone-number)

(defn number [s]
  {:post [(= (count %) 10)]}
  (let [s (apply str (filter #(Character/isDigit %) s))
        cnt (count s)]
      (= 10 cnt) s
      (and (= 11 cnt) (= \1 (first s))) (subs s 1)
      :else "0000000000")))

(defn area-code [s]
  (subs (number s) 0 3))

(defn prefix [s]
  (subs (number s) 3 6))

(defn line [s]
  (subs (number s) 6 10))

(defn pretty-print [s]
  (format "(%s) %s-%s" (area-code s) (prefix s) (line s)))

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