Lua solution for week 100, part 1

2 files changed, 57 insertions, 0 deletions

diff --git a/challenge-100/abigail/README.md b/challenge-100/abigail/README.md
index d4f0bcee6b..c3d1134d80 100644
--- a/challenge-100/abigail/README.md
+++ b/challenge-100/abigail/README.md
@@ -22,6 +22,7 @@ Output: 07:15 pm or 07:15pm
 * [Bash](bash/ch-1.sh)
 * [Befunge-93](befunge-93/ch-1.bf93)
 * [C](c/ch-1.c)
+* [Lua](lua/ch-1.lua)
 * [Perl](perl/ch-1.pl)
 
 ### Blog
diff --git a/challenge-100/abigail/lua/ch-1.lua b/challenge-100/abigail/lua/ch-1.lua
new file mode 100644
index 0000000000..6e0f3a721a
--- /dev/null
+++ b/challenge-100/abigail/lua/ch-1.lua
@@ -0,0 +1,56 @@
+#!/opt/local/bin/lua
+
+--
+-- See ../README.md
+--
+
+--
+-- Run as: lua ch-1.lua < input-file
+--
+
+for line in io . lines () do
+    --
+    -- Parse input
+    --
+    local _, _, hour, minute, ampm = line : find ("(%d+):(%d+)%s*([ap]?)m?")
+
+    --
+    -- We need an explicite case to numbers
+    --
+    hour   = tonumber (hour)
+    minute = tonumber (minute)
+
+    --
+    -- Find out what the new AM/PM marker should be:
+    --   - If the current marker is AM or PM, the new one is empty.
+    --   - Else, if the hour is 12 or higher, it's PM
+    --   - Else, it's AM
+    --
+    local new_ampm = ""
+    if   ampm == ""
+    then if   hour >= 12
+         then new_ampm = "pm"
+         else new_ampm = "am"
+         end
+    end
+
+    --
+    -- Calculate the new hours
+    --   - If AM, an hour of 12 becomes 0, and we leave the rest as is
+    --   - If PM, an hour of 12 stays 12, else, we add 12 to the hour
+    --   - If no AM/PM, subtract 12 if the hour is larger than 12;
+    --        add 12 if the hour is 0
+    --
+    hour = hour % 12
+    if   ampm == "" and hour == 0
+    then hour = 12
+    end
+    if   ampm == "p"
+    then hour = hour + 12
+    end
+
+    --
+    -- Print the results
+    --
+    print (string . format ("%02d:%02d%s", hour, minute, new_ampm))
+end