Solve AOC day 3 pt 1

projects/aoc/src/year2021/Solutions2021.kiss

@@ -9,7 +9,10 @@
         (load "day2.kiss")
         (assert (= 2150351 (apply * (simulateSubCommands (readSubCommands "src/year2021/inputs/day2.txt")))))
         (assert (= 1842742223 (apply * (simulateSubCommands (readSubCommands "src/year2021/inputs/day2.txt") true)))))
-    (dayTodo 3)
+    (day 3
+        (load "day3.kiss")
+        (let [inputs (Util.readLines "src/year2021/inputs/day3.txt")]
+            (assert (= 845186 (* (rate inputs false) (rate inputs true))))))
     (dayTodo 4)
     (dayTodo 5)
     (dayTodo 6)

projects/aoc/src/year2021/day3.kiss

@@ -0,0 +1,28 @@
+// Silly but fun implementation of a binary->decimal conversion
+(function :Int binaryStringToDecimal [:String binary &opt :Bool invert]
+    (apply +
+        (for [idx digit] (enumerate (reversed (binary.split "")))
+            (* 
+                (let [digit (Std.parseInt digit)] (if invert (- 1 digit) digit))
+                (^ 2 idx)))))
+
+(assert (= 22 (binaryStringToDecimal "10110")))
+(assert (= 9 (binaryStringToDecimal "10110" true)))
+
+(function :String mostCommonBit [:String binary]
+    (let [&mut ones 0.0
+            &mut total 0.0]
+        (doFor digit (binary.split "")
+            (+= total 1)
+            (case digit
+                ("1" (+= ones 1))
+                (otherwise)))
+        (Std.string (Math.round (/ ones total)))))
+
+(function :Int rate [:Array<String> inputs :Bool epsilon]
+    (binaryStringToDecimal
+        (.join
+            (for idx (range .length (first inputs))
+                (mostCommonBit (.join (for input inputs (input.charAt idx)) "")))
+            "")
+        epsilon))