lua solution is in

2022/d4/d4.lua

@@ -0,0 +1,62 @@
+-- What we've learn:
+-- - [x] Open a file as read (same signature as python's open(<file>[, mode]))
+-- - [x] Read file line-by-line
+-- - [x] Lua's iterator can be a generator function
+-- - [x] string -> number with tonumber()
+-- - [x] Syntactic sugar on collection length (or any that implements :len()): #<var>
+-- - [x] `print(..args)`; printing a nil yields an empty space. print also formats as a fancy table
+--             ```
+--             > print(1,2,3,4)
+--             1       2       3       4
+--             > print(100, 200, 300, 400)
+--             100     200     300     400
+--             ```
+-- - [x] CLI arguments are globally `arg`. arg[0] is the location of script, arg[1] is the first cli arg
+-- - [x] There is no loop-`continue` in Lua
+
+local function main(file_loc)
+    counter = 0
+    for group in io.lines(file_loc) do
+        if #group > 0 then -- a better way is to strip the string first, idk how to do this, though
+            -- despite the fact that we establish the token consists of digits
+            -- Lua parses the token as "string" type.
+            time_matches = group:gmatch("%d+") 
+            l_begin = tonumber(time_matches())
+            l_end = tonumber(time_matches())
+            r_begin = tonumber(time_matches())
+            r_end = tonumber(time_matches())
+            -- check if one elf's time is contained within the other
+            -- 4       9       10      97
+            if (l_begin <= r_begin and r_end <= l_end) or 
+                (r_begin <= l_begin and l_end <= r_end) then
+                counter = counter + 1
+            end
+        end
+    end
+    print("part 1 " .. counter) -- print("part 1", counter) works as well. Guess it's var-args
+
+
+    counter = 0
+    for group in io.lines(file_loc) do
+        if #group > 0 then -- a better way is to strip the string first, idk how to do this, though
+            time_matches = group:gmatch("%d+")
+            l_begin = tonumber(time_matches())
+            l_end = tonumber(time_matches())
+            r_begin = tonumber(time_matches())
+            r_end = tonumber(time_matches())
+
+            -- check if one elf's time is contained within the other
+            if (l_begin >= r_begin and l_begin <= r_end) or -- l_begin within r's range
+               (r_begin >= l_begin and r_begin <= l_end) or -- r_begin within l's range
+               (l_end >= r_begin and l_end <= r_end) or -- l_end within r's range
+               (r_end >= l_begin and r_end <= l_end) -- r_end within l's range
+            then
+                counter = counter + 1
+            end
+        end
+    end
+    print("part 2 " .. counter)
+end
+
+main(arg[1])
+

2022/d4/flake.nix

@@ -13,7 +13,7 @@
           echo "The input files should be placed under ./data/{submission,example}.txt
           echo "This problem shares one input between two parts"
         '';
-        py_pkgs = [ pkgs.python39 ];
+        py_pkgs = [ pkgs.python310 ];
         lua_pkgs = [ (pkgs.lua.withPackages (luapkgs: [ luapkgs.busted luapkgs.luafilesystem ])) ];
       in
       {

2022/d4/run-lua.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env sh
+
+echo "example"
+lua d4.lua "./data/example.txt"
+
+echo "submission"
+lua d4.lua "./data/submission.txt"
+