move 2021 days to folder; update README

2 files changed, 61 insertions, 0 deletions

diff --git a/year2021/day3/part1.clj b/year2021/day3/part1.clj
new file mode 100644
index 0000000..3fe888e
--- /dev/null
+++ b/year2021/day3/part1.clj
@@ -0,0 +1,25 @@
+(require '[clojure.string :as str])
+
+(->> "./in"
+     (slurp)
+     (str/split-lines)
+     (map (fn [l] (map #(if (= % \1) 1 0) l)))
+     (apply (partial map +))
+     (map #(if (< % 500) \1 \0))
+     (str/join)
+     (#(Integer/parseInt % 2))
+     (#(* % (bit-xor % (dec (int (Math/pow 2 12))))))
+     (println)
+     )
+
+; (->> input data file name
+;      read in entire contents
+;      split contents into array of lines
+;      for each line, transform characters '1'/'0' to numbers
+;      build sum array using the lines
+;      convert back to array of characters
+;      join characters into single string
+;      convert binary string to a number (gamma)
+;      multiply gamma by its bit-inverse (bit length hard-coded)
+;      print results
+
diff --git a/year2021/day3/part2.clj b/year2021/day3/part2.clj
new file mode 100644
index 0000000..00e656f
--- /dev/null
+++ b/year2021/day3/part2.clj
@@ -0,0 +1,36 @@
+(require '[clojure.string :as str])
+
+(def bitcount 12)
+(def input
+  (->> "./in"
+      (slurp)
+      (str/split-lines)
+      (map #(Integer/parseInt % 2))
+      )
+  )
+
+(defn countbit [lst bit]
+  (->> lst
+       (map #(if (bit-test % bit) 1 0))
+       (apply +)
+       )
+  )
+
+(defn filterbit [lst bit v]
+  (if (= 1 (count lst))
+    lst
+    (filter #(= (bit-test % bit) v) lst)
+    )
+  )
+
+(loop [bit (dec bitcount) lst0 input lst1 input]
+  (if (and (= 1 (count lst0)) (= 1 (count lst1)))
+    (println (map * lst0 lst1))
+    (recur
+      (dec bit)
+      (filterbit lst0 bit (>= (countbit lst0 bit) (/ (count lst0) 2)))
+      (filterbit lst1 bit (< (countbit lst1 bit) (/ (count lst1) 2)))
+      )
+    )
+  )
+