structured data done.

src/structured_data.clj

@@ -1,16 +1,28 @@
 (ns structured-data)
 
+(defn train
+  []
+  (println "Choo choo!"))
+
 (defn do-a-thing [x]
-  :-)
+  (let [x2 (+ x x)]
+    (Math/pow x2 x2)))
 
 (defn spiff [v]
-  :-)
+  (let [first (get v 0)
+        third (get v 2)]
+    (if (or (nil? first) (nil? third))
+      nil
+      (+ first third))))
 
 (defn cutify [v]
-  :-)
+  (conj v "<3"))
 
 (defn spiff-destructuring [v]
-  :-)
+  (let [[first _ third] v]
+    (if (or (nil? first) (nil? third))
+      nil
+      (+ first third))))
 
 (defn point [x y]
   [x y])
@@ -19,96 +31,115 @@
   [bottom-left top-right])
 
 (defn width [rectangle]
-  :-)
+  (let [[[x1] [x2]] rectangle]
+    (- x2 x1)))
 
 (defn height [rectangle]
-  :-)
+  (let [[[_ y1] [_ y2]] rectangle]
+    (- y2 y1)))
 
 (defn square? [rectangle]
-  :-)
+  (= (width rectangle) (height rectangle)))
 
 (defn area [rectangle]
-  :-)
+  (let [[[x1 y1] [x2 y2]] rectangle]
+    (* (- x2 x1) (- y2 y1))))
 
 (defn contains-point? [rectangle point]
-  :-)
+  (let [[[x1 y1] [x2 y2]] rectangle
+        [x y] point]
+   (and (<= x1 x x2) (<= y1 y y2))))
 
 (defn contains-rectangle? [outer inner]
-  :-)
+  (let [[p1 p2] inner]
+    (and (contains-point? outer p1) (contains-point? outer p2))))
 
 (defn title-length [book]
-  :-)
+  (count (:title book)))
 
 (defn author-count [book]
-  :-)
+  (count (:authors book)))
 
 (defn multiple-authors? [book]
-  :-)
+  (> (author-count book) 1))
 
 (defn add-author [book new-author]
-  :-)
+  (let [authors (:authors book)]
+    (assoc book :authors (conj authors new-author))))
 
 (defn alive? [author]
-  :-)
+  (not (contains? author :death-year)))
 
 (defn element-lengths [collection]
-  :-)
+  (map count collection))
 
 (defn second-elements [collection]
-  :-)
+  (let [second (fn [coll] (first (rest coll)))]
+    (map second collection)))
 
 (defn titles [books]
-  :-)
+  (map :title books))
 
 (defn monotonic? [a-seq]
-  :-)
+  (or (apply >= a-seq) (apply <= a-seq)))
 
 (defn stars [n]
-  :-)
+  (apply str (repeat n "*")))
 
 (defn toggle [a-set elem]
-  :-)
+  (if (contains? a-set elem)
+    (disj a-set elem)
+    (conj a-set elem)))
 
 (defn contains-duplicates? [a-seq]
-  :-)
+  (not (= (count a-seq) (count (set a-seq)))))
 
 (defn old-book->new-book [book]
-  :-)
+  (let [new-authors (set (:authors book))]
+    (assoc book :authors new-authors)))
 
 (defn has-author? [book author]
-  :-)
+  (contains? (:authors book) author))
 
 (defn authors [books]
-  :-)
+  (apply clojure.set/union (map :authors books)))
 
 (defn all-author-names [books]
-  :-)
+  (set (map :name (authors books))))
 
 (defn author->string [author]
-  :-)
+  (let [name  (:name author)
+        birth-year (:birth-year author)
+        death-year (:death-year author)
+        years (if birth-year (str "(" birth-year " - " death-year ")"))]
+    (if years (str name " " years) name)))
 
 (defn authors->string [authors]
-  :-)
+  (apply str (interpose ", " (map author->string authors))))
 
 (defn book->string [book]
-  :-)
+  (str (:title book) ", written by " (authors->string (:authors book))))
 
 (defn books->string [books]
-  :-)
+  (let [num-books (count books)
+        zero-books (= 0 num-books)]
+    (if zero-books
+      "No books."
+      (str num-books (if (= 1 num-books) " book. " " books. ") (apply str (interpose ". " (map book->string books))) "."))))
 
 (defn books-by-author [author books]
-  :-)
+  (filter (fn [book] (has-author? book author)) books))
 
 (defn author-by-name [name authors]
-  :-)
+  (first (filter (fn [author] (= name (:name author))) authors)))
 
 (defn living-authors [authors]
-  :-)
+  (filter alive? authors))
 
 (defn has-a-living-author? [book]
-  :-)
+  (not (empty? (living-authors (:authors book)))))
 
 (defn books-by-living-authors [books]
-  :-)
+  (filter has-a-living-author? books))
 
 ; %________%