create ordered sequence of the given ranges' start and end values

src/challenge/discrete_value_range.clj

@@ -27,4 +27,28 @@
   (value-before [this])
   (value-after [this])
   (start [this])
-  (end [this]))
+  (end [this])
+  (range-type [this]))
+
+(defn- ordered-range-values
+  "Builds an ordered list or 'fenceposts' for the start and end
+  of all given ranges, to prepare to produces a consolidated
+  set of ranges, by doing open/close count matching.
+
+  By building this list, it will allow us to push a `start`
+  onto a stack, and `pop` when we encounter an `end.`
+
+  If we pop, and get an empty stack, we have found the item
+  that represents the end value that matches the start value
+  that we just popped off the stack, and are able to ignore
+  any intermediate matching starts/stops."
+  [ranges]
+  (->> ranges
+       (mapcat (fn [range]
+                 [{:value (start range)
+                   :boundary-type :start
+                   :type (range-type range)}
+                  {:value (end range)
+                   :boundary-type :end
+                   :type (range-type range)}]))
+       (sort-by (juxt :value (comp {:start 0 :end 1} :boundary-type)))))