Solve day 1 part 2

day_1.sml

@@ -25,7 +25,20 @@ val lists = (
     sortAsc (map (fn (pair) => List.last pair) pairs)
 )
 
+(* Part 1 *)
+
 val distances = ListPair.map (fn (n1, n2) => abs(n1 - n2)) lists
 
 val totalDistance = sum distances
 
+(* Part 2 *)
+
+val similarities = ListPair.map
+    (fn (n1, n2) =>
+        let val frequency = List.length (List.filter (fn (n) => n = n1) (#2 lists))
+        in n1 * frequency end
+    )
+    lists
+
+val similarityScore = sum similarities
+