Binary search: Sync metadata docs, implement tests, update example solution

exercises/practice/binary-search/.docs/instructions.md

@@ -11,7 +11,7 @@ Binary search only works when a list has been sorted.
 
 The algorithm looks like this:
 
-- Find the middle element of a *sorted* list and compare it with the item we're looking for.
+- Find the middle element of a _sorted_ list and compare it with the item we're looking for.
 - If the middle element is our item, then we're done!
 - If the middle element is greater than our item, we can eliminate that element and all the elements **after** it.
 - If the middle element is less than our item, we can eliminate that element and all the elements **before** it.

exercises/practice/binary-search/.meta/config.json

@@ -24,5 +24,5 @@
   },
   "blurb": "Implement a binary search algorithm.",
   "source": "Wikipedia",
-  "source_url": "http://en.wikipedia.org/wiki/Binary_search_algorithm"
+  "source_url": "https://en.wikipedia.org/wiki/Binary_search_algorithm"
 }

exercises/practice/binary-search/.meta/src/example.clj

@@ -1,14 +1,15 @@
 (ns binary-search)
 
-(defn middle [alist]
-  (-> alist (count) (quot 2)))
-
 (defn search-for
-  [elem alist]
-  (let [middle (middle alist)
-        cur-elem (nth alist middle)]
-    (cond
-      (= cur-elem elem) middle
-      (or (= middle (count alist)) (zero? middle)) (throw (Exception. (format "%s not found in list" elem)))
-      (< cur-elem elem) (+ middle (search-for elem (drop middle alist)))
-      (> cur-elem elem) (search-for elem (take middle alist)))))
+  [n coll]
+  (let [coll (vec coll)]
+    (loop [low-idx 0
+           high-idx (dec (count coll))]
+      (if (> low-idx high-idx)
+        (throw (Exception. "not found"))
+        (let [mid-index (quot (+ high-idx low-idx) 2)
+              mid-item (get coll mid-index)]
+          (cond
+            (= n mid-item) mid-index
+            (> mid-item n) (recur low-idx (dec mid-index))
+            :else (recur (inc mid-index) high-idx)))))))

exercises/practice/binary-search/test/binary_search_test.clj

@@ -1,40 +1,52 @@
 (ns binary-search-test
-  (:require [clojure.test :refer [deftest is]]
+  (:require [clojure.test :refer [deftest is testing]]
             binary-search))
 
-(def short-vector [1, 3, 4, 6, 8, 9, 11])
-
-(def large-vector [1, 3, 5, 8, 13, 21, 34, 55, 89])
-
-(def even-length-vector [1, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377])
-
-(deftest it-finds-position-of-middle-item
-  (is (= 3 (binary-search/middle short-vector))))
-
-(deftest searches-a-singleton
-  (is (= 0 (binary-search/search-for 4 [4]))))
-
-(deftest it-finds-position-of-search-data
-  (is (= 5 (binary-search/search-for 9 short-vector))))
-
-(deftest it-finds-position-in-a-larger-list
-  (is (= 1 (binary-search/search-for 3 large-vector))))
-
-(deftest it-finds-position-in-a-larger-list-again
-  (is (= 7 (binary-search/search-for 55 large-vector))))
-
-(deftest it-finds-correct-position-in-a-list-with-an-even-number-of-elements
-  (is (= 5 (binary-search/search-for 21 even-length-vector))))
-
-(deftest it-finds-correct-position-in-a-list-with-an-even-number-of-elements-again
-  (is (= 6 (binary-search/search-for 34 even-length-vector))))
-
-(deftest it-works-on-lists
-  (is (= 7 (binary-search/search-for 7 (range 10)))))
-
-(deftest it-works-on-lists-again
-  (is (= 4 (binary-search/search-for 3 '(-3 -2 0 1 3 4)))))
-
-(deftest throws-exception-when-element-not-found
-  (is (thrown-with-msg? Throwable #"not found"
-                        (binary-search/search-for 20 short-vector))))
+(deftest finds-value-in-array-with-one-element
+  (testing "Finds a value in an array with one element"
+           (is (= 0 (binary-search/search-for 6 [6])))))
+
+(deftest finds-value-in-middle-of-array
+  (testing "Finds a value in the middle of an array"
+    (is (= 3 (binary-search/search-for 6 [1, 3, 4, 6, 8, 9, 11])))))
+
+(deftest finds-value-at-beginning-of-array
+  (testing "Finds a value at the beginning of an array"
+    (is (= 0 (binary-search/search-for 1 [1, 3, 4, 6, 8, 9, 11])))))
+
+(deftest finds-value-at-end-of-array
+  (testing "Finds a value at the end of an array"
+    (is (= 6 (binary-search/search-for 11 [1, 3, 4, 6, 8, 9, 11])))))
+
+(deftest finds-value-in-array-of-odd-length
+  (testing "Finds a value in an array of odd length"
+    (is (= 9 (binary-search/search-for 144 [1, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 634])))))
+
+(deftest finds-value-in-array-of-even-length
+  (testing "Finds a value in an array of even length"
+    (is (= 5 (binary-search/search-for 21 [1, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377])))))
+
+(deftest identifies-that-value-is-not-in-array
+  (testing "Identifies that a value is not included in the array"
+    (is (thrown-with-msg? Throwable #"not found"
+                          (binary-search/search-for 7 [1, 3, 4, 6, 8, 9, 11])))))
+
+(deftest value-smaller-than-arrays-smallest-value-not-found
+  (testing "A value smaller than the array's smallest value is not found"
+    (is (thrown-with-msg? Throwable #"not found"
+                          (binary-search/search-for 0 [1, 3, 4, 6, 8, 9, 11])))))
+
+(deftest value-larger-than-arrays-largest-value-not-found
+  (testing "A value larger than the array's largest value is not found"
+    (is (thrown-with-msg? Throwable #"not found"
+                          (binary-search/search-for 13 [1, 3, 4, 6, 8, 9, 11])))))
+
+(deftest nothing-found-in-empty-array
+  (testing "Nothing is found in an empty array"
+    (is (thrown-with-msg? Throwable #"not found"
+                          (binary-search/search-for 1 [])))))
+
+(deftest nothing-found-when-left-and-right-bounds-cross
+  (testing "Nothing is found when the left and right bounds cross"
+    (is (thrown-with-msg? Throwable #"not found"
+                          (binary-search/search-for 0 [1, 2])))))