feat: solve day 4 puzzle 1

src/day04/puzzle1.lua

@@ -0,0 +1,44 @@
+local utils = require "utils"
+
+local puzzle1 = {}
+
+function puzzle1.inGrid(x, y, w, h)
+    return 1 <= x and x <= w and 1 <= y and y <= h
+end
+
+function puzzle1.isAccessible(lines, w, h, x, y)
+    local neighbors = 0
+    for dy=-1, 1 do
+        for dx=-1, 1 do
+            if dx ~=0 or dy ~= 0 then
+                local x2 = x + dx
+                local y2 = y + dy
+                if puzzle1.inGrid(x2, y2, w, h) then
+                    if lines[y2]:sub(x2, x2) == "@" then
+                        neighbors = neighbors + 1
+                    end
+                end
+            end
+        end
+    end
+    return neighbors < 4
+end
+
+function puzzle1.solve(input)
+    local lines = utils.splitLines(input)
+    local accessible = 0
+
+    local h = #lines
+    local w = #lines[1]
+
+    for y, line in ipairs(lines) do
+        for x=1, #line do
+            if line:sub(x, x) == "@" and puzzle1.isAccessible(lines, w, h, x, y) then
+                accessible = accessible + 1
+            end
+        end
+    end
+    return accessible
+end
+
+return puzzle1

src/day04/puzzle2.lua

@@ -0,0 +1,7 @@
+local puzzle2 = {}
+
+function puzzle2.solve(input)
+    return 0
+end
+
+return puzzle2