Task 2

3 files changed, 24 insertions, 7 deletions

diff --git a/challenge-075/tyler-wardhaugh/clojure/README.md b/challenge-075/tyler-wardhaugh/clojure/README.md
index 8c07634ced..4bc8af0088 100644
--- a/challenge-075/tyler-wardhaugh/clojure/README.md
+++ b/challenge-075/tyler-wardhaugh/clojure/README.md
@@ -19,7 +19,7 @@ Run Task #1 with input (SUM COIN [COIN]...)
 
 Run Task #2 with input:
 
-    $ clojure -m tw.weekly.ch-2 "asdjfklsfasdjfklq"
+    $ clojure -m tw.weekly.ch-2 2 1 4 5 3 7
 
 ## Project Template
 
diff --git a/challenge-075/tyler-wardhaugh/clojure/src/tw/weekly/ch_2.clj b/challenge-075/tyler-wardhaugh/clojure/src/tw/weekly/ch_2.clj
index a71ab930c4..72a4e05269 100644
--- a/challenge-075/tyler-wardhaugh/clojure/src/tw/weekly/ch_2.clj
+++ b/challenge-075/tyler-wardhaugh/clojure/src/tw/weekly/ch_2.clj
@@ -1,10 +1,27 @@
 (ns tw.weekly.ch-2
   (:require [clojure.edn :as edn]))
 
+; algorithm source: https://stackoverflow.com/a/35931960
+;   Answer by Spectral (https://stackoverflow.com/users/2558887/spectral)
+;   (modified from Python)
+
+(defn largest-rectangle-histogram
+  "Compute the area of the largest possible rectangle within a histogram."
+  [hist]
+  (let [decorated (into [] (concat [-1] hist [-1]))
+         stack (atom (list [0 (first decorated)]))
+         max-area (atom 0)]
+     (reduce-kv (fn [ans k v]
+                  (while (< v (-> @stack peek last))
+                    (let [head (-> (swap-vals! stack pop) first peek last)
+                          area (* head (- k (-> @stack peek first) 1))]
+                      (swap! max-area max area)))
+                  (swap! stack conj [k v])
+                  (max ans @max-area))
+                0 decorated)))
+
 (defn -main
   "Run Task 2 with a list of integers, defaulting to the sample given in the task description."
   [& args]
   (let [A (if (not-empty args) (map edn/read-string args) [2, 1, 4, 5, 3, 7])]
-    (println A)))
-
-(-main)
+    (prn (largest-rectangle-histogram A))))
diff --git a/challenge-075/tyler-wardhaugh/clojure/test/tw/weekly/c75_test.clj b/challenge-075/tyler-wardhaugh/clojure/test/tw/weekly/c75_test.clj
index 856991c00c..c9121cd68a 100644
--- a/challenge-075/tyler-wardhaugh/clojure/test/tw/weekly/c75_test.clj
+++ b/challenge-075/tyler-wardhaugh/clojure/test/tw/weekly/c75_test.clj
@@ -2,7 +2,7 @@
   (:require [clojure.test :refer :all]
             [multiset.core :as ms]
             [tw.weekly.ch-1 :refer [find-coin-sum]]
-            [tw.weekly.ch-2 :refer []]))
+            [tw.weekly.ch-2 :refer [largest-rectangle-histogram]]))
 
 (deftest ch-1
   (testing "Task 1"
@@ -11,5 +11,5 @@
 
 (deftest ch-2
   (testing "Task 2"
-    
-    ))
+    (is (= 12 (largest-rectangle-histogram [2 1 4 5 3 7])))
+    (is (= 15 (largest-rectangle-histogram [3 2 3 5 7 5])))))