day 10 puzzle 2

progress.yaml

@@ -17,4 +17,4 @@
 9:
   stars: 2
 10:
-  stars: 1
+  stars: 2

src/day10/puzzle2.typ

@@ -1,11 +1,74 @@
 #import "/src/utils.typ": *
+#let offsets = (
+  (-1, 0),
+  (0, -1),
+  (1, 0),
+  (0, 1)
+)
+
+#let in-grid(w, h, x, y) = {
+  return 0 <= x and x < w and 0 <= y and y < h
+}
+
+#let count-paths(grid, w, h, ox, oy) = {
+  let in-grid = in-grid.with(w, h)
+  let rating = 0
+
+  let to-visit = ((ox, oy),)
+  while to-visit.len() != 0 {
+    let (x, y) = to-visit.remove(0)
+    let v = grid.at(y).at(x)
+    let branches = 0
+    for (dx, dy) in offsets {
+      let (x2, y2) = (x + dx, y + dy)
+      if not in-grid(x2, y2) {
+        continue
+      }
+      let v2 = grid.at(y2).at(x2)
+      if v2 == v + 1 {
+        let pos2 = (x2, y2)
+        branches += 1
+        if v2 != 9 {
+          to-visit.push(pos2)
+        }
+      }
+    }
+    rating += if v == 0 {
+      branches
+    } else {
+      branches - 1  // If no branch -> -1
+    }
+  }
+
+  return rating
+}
 
 #let solve(input) = {
+  let grid = input.split("\n").map(l => l.clusters().map(int))
 
+  let w = grid.first().len()
+  let h = grid.len()
+
+  let count-paths = count-paths.with(grid, w, h)
+
+  let ratings = ()
+  let total = 0
+  for y in range(h) {
+    for x in range(w) {
+      if grid.at(y).at(x) == 0 {
+        let rating = count-paths(x, y)
+        total += rating
+        ratings.push(rating)
+      }
+    }
+  }
+  let a = ratings
+
+  return total
 }
 
 #show-puzzle(
   10, 2,
   solve,
-  example: 0
+  example: 81
 )