anonymous_letter.clj

(ns anonymous-letter.core-test
  (:require [clojure.test :refer :all]
            [anonymous-letter.core :refer :all]))

(defn decrement-dict [word dictionary]
  (conj dictionary 
        [word
         (dec (let [count (get dictionary word)] 
                (if (nil? count) 0 count)))]))

(defn can-write-letter [words-in-letter dictionary]
  (loop [words words-in-letter
         current-dictionary dictionary
         result true]
    (let [[first-word] words]
      (if (nil? first-word) 
        result
        (let [is-in-dictionary (let [count (get dictionary first-word)] 
                                 (if (nil? count) false (> count 0)))]
          (recur (rest words) 
                 (decrement-dict first-word current-dictionary) 
                 is-in-dictionary))))))

(deftest a-test
  (testing "single word in dictionary"
    (is (= (can-write-letter ["hello"] {"hello" 1}) true))))

(deftest b-test
  (testing "single word not in dictionary"
    (is (= (can-write-letter ["hello"] {"world" 1}) false))))

(deftest c-test
  (testing "one word in dictionary but the second is not"
    (is (= (can-write-letter ["hello" "world"] {"hello" 1}) false))))