added visualization for day 4 puzzle 2

src/day4/puzzle2.typ

@@ -1,4 +1,5 @@
 #import "/src/utils.typ": *
+#import "@preview/cetz:0.3.1": canvas, draw
 
 #let solve(input) = {
   let lines = input.split("\n")
@@ -26,8 +27,62 @@
   return total
 }
 
+#let visualize(input) = {
+  let lines = input.split("\n")
+  let w = lines.first().len()
+  let h = lines.len()
+
+  let perms = (("M", "S"), ("S", "M"))
+  let positions = ()
+  for y in range(1, h - 1) {
+    for x in range(1, w - 1) {
+      if lines.at(y).at(x) == "A" {
+        let tl = lines.at(y - 1).at(x - 1)
+        let tr = lines.at(y - 1).at(x + 1)
+        let bl = lines.at(y + 1).at(x - 1)
+        let br = lines.at(y + 1).at(x + 1)
+        let tlbr = (tl, br)
+        let bltr = (bl, tr)
+        if tlbr in perms and bltr in perms {
+          positions.push((x, y))
+        }
+      }
+    }
+  }
+
+  canvas({
+    for y in range(h) {
+      for x in range(w) {
+        let valid = (x, y) in positions
+        if valid {
+          draw.circle(
+            (x, y),
+            radius: 0.3,
+            stroke: red,
+            name: str(x) + "-" + str(y)
+          )
+          for dy in (-1, 1) {
+            for dx in (-1, 1) {
+              draw.line(
+                str(x) + "-" + str(y),
+                (x + dx * 0.75, y + dy * 0.75),
+                stroke: red
+              )
+            }
+          }
+        }
+        draw.content(
+          (x, y),
+          lines.at(y).at(x)
+        )
+      }
+    }
+  })
+}
+
 #show-puzzle(
   4, 2,
   solve,
-  example: 9
+  example: 9,
+  visualize: visualize
 )