2 files changed, 85 insertions, 0 deletions
diff --git a/aoc/2021/day03/input.txt b/aoc/2021/day03/input.txt
new file mode 100644
index 0000000..a6366a8
--- /dev/null
+++ b/aoc/2021/day03/input.txt
@@ -0,0 +1,12 @@
+00100
+11110
+10110
+10111
+10101
+01111
+00111
+11100
+10000
+11001
+00010
+01010
diff --git a/aoc/2021/day03/part1.neb b/aoc/2021/day03/part1.neb
new file mode 100644
index 0000000..7ca6a08
--- /dev/null
+++ b/aoc/2021/day03/part1.neb
@@ -0,0 +1,73 @@
+;; https://adventofcode.com/2021/day/3
+
+(func one-most-common (inp)
+    (>
+        (length
+            (filter (lambda (x) (eq? "1" x)) inp))
+        (/ (length inp) 2)))
+
+; treating bits as a string of 1s and 0s
+; note: for this problem, even if neb had byte things,
+; strings would probably still be the way to go
+(func bit-flip (bitstr)
+    (join
+        (map
+            (lambda (x) (if (eq? "0" x) "1" "0"))
+            (split bitstr))
+        ""))
+
+; 'exp' or something should be in the stdlib
+(func two-n (n)
+    (branch
+        ((eq? 0 n) 1)
+        ((eq? 1 n) 2)
+        (#true
+            (* 2 (two-n (- n 1))))))
+
+(func parse-binary (bitstr)
+    (parse-binary bitstr 0 0))
+
+(func parse-binary (bitstr pos acc)
+    (if (eq? 0 (length bitstr))
+        acc
+        (block
+            (def next-int (string->int (last bitstr)))
+            (if (eq? 0 next-int)
+                (parse-binary
+                    (most bitstr)
+                    (+ 1 pos)
+                    acc)
+                (parse-binary
+                    (most bitstr)
+                    (+ 1 pos)
+                    (+ acc
+                        (two-n pos)))))))
+                        ;(* 2 pos)))))))
+
+(func do-the-thing (inp)
+    ; i don't like the def/redef pattern
+    ; this would benefit from something like "gather"
+    ; this might also work as a map/reduce?
+    (def out "")
+    (for-count (length (first inp))
+        (def one?
+            (one-most-common 
+                (map
+                    (lambda (x)
+                        (first (slice x _idx_ 1)))
+                    inp)))
+        (redef out
+            (concat out
+                (if one? "1" "0"))))
+    (print (->string
+        (* 
+            (parse-binary out)
+            (parse-binary (bit-flip out)))))
+    )
+
+(def lines 
+    (map split  ; get all numbers as list of chars
+        (map strip
+            (read-lines "input.txt"))))
+
+(do-the-thing lines)