1 files changed, 36 insertions, 0 deletions
diff --git a/challenge-119/abigail/lua/ch-2.lua b/challenge-119/abigail/lua/ch-2.lua
new file mode 100644
index 0000000000..e0c940767d
--- /dev/null
+++ b/challenge-119/abigail/lua/ch-2.lua
@@ -0,0 +1,36 @@
+#!/opt/local/bin/lua
+
+--
+-- See ../README.md
+--
+
+--
+-- Run as: lua ch-2.lua < input-file
+--
+
+function next_number (prev_num)
+    --
+    -- Get the trailing 3s (tail), and the number before (num)
+    -- and anything before it (prefix)
+    --
+    local _, _, prefix, num, tail =
+        ("0" .. prev_num) : find ("(.*)([012])(3*)$")
+
+    --
+    -- Combine the prefix, num (with 1 added) and the tail (with
+    -- its 3s replaced by 1s), then in the result, replace each '11'
+    -- with '12', and remove the leading 0 (if any).
+    --
+    return (prefix .. tostring (tonumber (num) + 1) 
+                   .. tail : gsub ("3", "1")) : gsub ("11", "12")
+                                              : gsub ("^0", "")
+end
+
+
+for num in io . lines () do
+    local number = "0"
+    for _ = 1, tonumber (num) do
+        number = next_number (number)
+    end
+    print (number)
+end