2020 day 25 (bash)

2020/day25/ex1.bash

@@ -0,0 +1,22 @@
+#!/bin/bash
+#
+# ex1.bash: Advent2020 game, day 25/game 1.
+
+CMD=${0##*/}
+shopt -s extglob
+set -o noglob
+
+declare -a pub=(1 1) enc=(1 1) key
+read -r "key[0]"
+read -r "key[1]"
+
+while true; do
+    ((pub[0] = (pub[0] * 7)      % 20201227,
+      pub[1] = (pub[1] * 7)      % 20201227,
+      enc[0] = (enc[0] * key[0]) % 20201227,
+      enc[1] = (enc[1] * key[1]) % 20201227))
+    ((pub[0] == key[0])) && res=${enc[1]} && break
+    ((pub[1] == key[1])) && res=${enc[0]} && break
+done
+printf "%s: res=%s\n" "$CMD" "$res"
+exit 0