Solutions for advent of code, day 4 - 13.

examples/advent2024/BUILD

@@ -9,50 +9,21 @@ utils = [
     "sort.carbon",
 ]
 
-carbon_binary(
-    name = "day1_part1",
-    srcs = [
-        "day1_common.carbon",
-        "day1_part1.carbon",
-    ] + utils,
-)
-
-carbon_binary(
-    name = "day1_part2",
-    srcs = [
-        "day1_common.carbon",
-        "day1_part2.carbon",
-    ] + utils,
-)
-
-carbon_binary(
-    name = "day2_part1",
-    srcs = [
-        "day2_common.carbon",
-        "day2_part1.carbon",
-    ] + utils,
-)
-
-carbon_binary(
-    name = "day2_part2",
-    srcs = [
-        "day2_common.carbon",
-        "day2_part2.carbon",
-    ] + utils,
-)
-
-carbon_binary(
-    name = "day3_part1",
-    srcs = [
-        "day3_common.carbon",
-        "day3_part1.carbon",
-    ] + utils,
-)
-
-carbon_binary(
-    name = "day3_part2",
-    srcs = [
-        "day3_common.carbon",
-        "day3_part2.carbon",
-    ] + utils,
-)
+# A list of examples that should be excluded because they don't build any more.
+# For example, to exclude day3_part2, use:
+# excluded = [(3, 2)]
+excluded = []
+
+# Produce a binary "dayX_partY" for each matching `.carbon` file.
+[
+    carbon_binary(
+        name = "day{0}_part{1}".format(day, part),
+        srcs = [
+            "day{0}_common.carbon".format(day),
+            "day{0}_part{1}.carbon".format(day, part),
+        ] + utils,
+    )
+    for day in range(1, 14)
+    for part in range(1, 3)
+    if (day, part) not in excluded
+]

examples/advent2024/README.md

@@ -15,3 +15,9 @@ style and idioms. Instead, the purpose of these examples are to test the current
 state of the toolchain against larger code examples than those that are present
 in the toolchain's own tests, to find bugs in the toolchain, and to drive
 feature development in the toolchain by presenting somewhat realistic testcases.
+
+If one of these examples stops building after a change to the toolchain, please:
+
+-   Make sure that the build break is an expected consequence of the change.
+-   Update the `BUILD` file to exclude that example.
+-   File an issue and assign it to @zygoloid.

examples/advent2024/day10_common.carbon

@@ -0,0 +1,29 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// https://adventofcode.com/2024/day/10
+
+library "day10_common";
+
+import Core library "io";
+import library "io_utils";
+
+class Terrain {
+  fn Read() -> Terrain {
+    returned var me: Terrain;
+    var y: i32 = 0;
+    while (y < 43) {
+      var x: i32 = 0;
+      while (x < 43) {
+        me.height[x][y] = ReadChar() - 0x30;
+        ++x;
+      }
+      SkipNewline();
+      ++y;
+    }
+    return var;
+  }
+
+  var height: [[i32; 43]; 43];
+}

examples/advent2024/day10_part1.carbon

@@ -0,0 +1,99 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// https://adventofcode.com/2024/day/10
+
+import Core library "io";
+
+import library "day10_common";
+import library "io_utils";
+
+// TODO: Add this to the prelude.
+fn PopCount(n: u256) -> i32 {
+  var bit: u256 = 1;
+  var total: i32 = 0;
+  while (bit != 0) {
+    if (n & bit != 0) {
+      ++total;
+    }
+    bit = bit << 1;
+  }
+  return total;
+}
+
+class Reachable {
+  fn Make(terrain: Terrain) -> Reachable {
+    returned var me: Reachable;
+    var next: u256 = 1;
+    var y: i32 = 0;
+    while (y < 43) {
+      var x: i32 = 0;
+      while (x < 43) {
+        if (terrain.height[x][y] == 0) {
+          me.trailheads[x][y] = next;
+          next = next << 1;
+        }
+        ++x;
+      }
+      ++y;
+    }
+    return var;
+  }
+
+  fn AddLevel[addr self: Self*](terrain: Terrain, level: i32) {
+    let adj: [(i32, i32); 4] = ((-1, 0), (0, -1), (1, 0), (0, 1));
+    var y: i32 = 0;
+    while (y < 43) {
+      var x: i32 = 0;
+      while (x < 43) {
+        if (terrain.height[x][y] == level) {
+          var reach: u256 = 0;
+          var i: i32 = 0;
+          while (i < 4) {
+            let adj_x: i32 = x + adj[i].0;
+            let adj_y: i32 = y + adj[i].1;
+            if (adj_x >= 0 and adj_x < 43 and
+                adj_y >= 0 and adj_y < 43 and
+                terrain.height[adj_x][adj_y] == level - 1) {
+              reach = reach | self->trailheads[adj_x][adj_y];
+            }
+            ++i;
+          }
+          self->trailheads[x][y] = reach;
+        }
+        ++x;
+      }
+      ++y;
+    }
+  }
+
+  fn Count[self: Self](terrain: Terrain, level: i32) -> i32 {
+    var total: i32 = 0;
+    var y: i32 = 0;
+    while (y < 43) {
+      var x: i32 = 0;
+      while (x < 43) {
+        if (terrain.height[x][y] == level) {
+          total += PopCount(self.trailheads[x][y]);
+        }
+        ++x;
+      }
+      ++y;
+    }
+    return total;
+  }
+
+  var trailheads: [[u256; 43]; 43];
+}
+
+fn Run() {
+  var terrain: Terrain = Terrain.Read();
+  var reachable: Reachable = Reachable.Make(terrain);
+  var i: i32 = 1;
+  while (i <= 9) {
+    reachable.AddLevel(terrain, i);
+    ++i;
+  }
+  Core.Print(reachable.Count(terrain, 9));
+}

examples/advent2024/day10_part2.carbon

@@ -0,0 +1,72 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// https://adventofcode.com/2024/day/10
+
+import Core library "io";
+
+import library "day10_common";
+import library "io_utils";
+
+class PathsToTop {
+  fn Make(terrain: Terrain) -> PathsToTop {
+    returned var me: PathsToTop;
+    var y: i32 = 0;
+    while (y < 43) {
+      var x: i32 = 0;
+      while (x < 43) {
+        // TODO: We shouldn't need an explicit cast here.
+        me.paths[x][y] =
+          if terrain.height[x][y] == 9 then 1 as i64 else 0;
+        ++x;
+      }
+      ++y;
+    }
+    return var;
+  }
+
+  fn AddLevel[addr self: Self*](terrain: Terrain, level: i32) -> i64 {
+    var total: i64 = 0;
+    let adj: [(i32, i32); 4] = ((-1, 0), (0, -1), (1, 0), (0, 1));
+    var y: i32 = 0;
+    while (y < 43) {
+      var x: i32 = 0;
+      while (x < 43) {
+        if (terrain.height[x][y] == level) {
+          var paths: i64 = 0;
+          var i: i32 = 0;
+          while (i < 4) {
+            let adj_x: i32 = x + adj[i].0;
+            let adj_y: i32 = y + adj[i].1;
+            if (adj_x >= 0 and adj_x < 43 and
+                adj_y >= 0 and adj_y < 43 and
+                terrain.height[adj_x][adj_y] == level + 1) {
+              paths = paths + self->paths[adj_x][adj_y];
+            }
+            ++i;
+          }
+          self->paths[x][y] = paths;
+          total = total + paths;
+        }
+        ++x;
+      }
+      ++y;
+    }
+    return total;
+  }
+
+  var paths: [[i64; 43]; 43];
+}
+
+fn Run() {
+  var terrain: Terrain = Terrain.Read();
+  var paths: PathsToTop = PathsToTop.Make(terrain);
+  var i: i32 = 8;
+  var total: i64;
+  while (i >= 0) {
+    total = paths.AddLevel(terrain, i);
+    --i;
+  }
+  PrintInt64(total);
+}

examples/advent2024/day11_common.carbon

@@ -0,0 +1,31 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// https://adventofcode.com/2024/day/11
+
+library "day11_common";
+
+import Core library "io";
+import library "io_utils";
+
+fn Next(n: i64) -> (i64, i64) {
+  if (n == 0) { return (1, -1); }
+  var pow10: i64 = 10;
+  var pow100: i64 = 1;
+  while (n / pow100 >= 100) {
+    pow100 = pow100 * 100;
+    pow10 = pow10 * 10;
+  }
+  if (n / pow100 >= 10) {
+    return (n / pow10, n % pow10);
+  }
+  return (n * 2024, -1);
+}
+
+fn Count(n: i64, depth: i32) -> i32 {
+  if (n == -1) { return 0; }
+  if (depth == 0) { return 1; }
+  let next: (i64, i64) = Next(n);
+  return Count(next.0, depth - 1) + Count(next.1, depth - 1);
+}

examples/advent2024/day11_part1.carbon

@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// https://adventofcode.com/2024/day/11
+
+import Core library "io";
+
+import library "day11_common";
+import library "io_utils";
+
+fn Run() {
+  var n: i64;
+  var total: i32 = 0;
+  while (ReadInt64(&n)) {
+    total = total + Count(n, 25);
+    SkipSpaces();
+  }
+  Core.Print(total);
+}