Solution for advent of code day 4.

examples/advent2024/BUILD

@@ -56,3 +56,19 @@ carbon_binary(
         "day3_part2.carbon",
     ] + utils,
 )
+
+carbon_binary(
+    name = "day4_part1",
+    srcs = [
+        "day4_common.carbon",
+        "day4_part1.carbon",
+    ] + utils,
+)
+
+carbon_binary(
+    name = "day4_part2",
+    srcs = [
+        "day4_common.carbon",
+        "day4_part2.carbon",
+    ] + utils,
+)

examples/advent2024/day4_common.carbon

@@ -0,0 +1,56 @@
+// 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
+
+library "day4_common";
+
+import library "io_utils";
+
+class Wordsearch {
+  fn Read() -> Wordsearch {
+    returned var s: Wordsearch;
+    // TODO: Use for loops once they're implemented.
+    var y: i32 = 0;
+    while (y < 140) {
+      var x: i32 = 0;
+      while (x < 140) {
+        // TODO: Assert on failure.
+        s.grid[x][y] = ReadChar();
+        ++x;
+      }
+      // TODO: Assert on failure.
+      SkipNewline();
+      ++y;
+    }
+    return var;
+  }
+
+  fn At[self: Self](x: i32, y: i32) -> i32 {
+    return if x < 0 or x >= 140 or y < 0 or y >= 140 then -1 else self.grid[x][y];
+  }
+
+  // TODO: Make this generic in the length of the search query.
+  fn Check4[self: Self](xmas: [i32; 4], x: i32, y: i32, dx: i32, dy: i32) -> bool {
+    var i: i32 = 0;
+    while (i < 4) {
+      if (self.At(x + i * dx, y + i * dy) != xmas[i]) {
+        return false;
+      }
+      ++i;
+    }
+    return true;
+  }
+
+  fn Check3[self: Self](mas: [i32; 3], x: i32, y: i32, dx: i32, dy: i32) -> bool {
+    var i: i32 = 0;
+    while (i < 3) {
+      if (self.At(x + i * dx, y + i * dy) != mas[i]) {
+        return false;
+      }
+      ++i;
+    }
+    return true;
+  }
+
+  var grid: [[i32; 140]; 140];
+}

examples/advent2024/day4_part1.carbon

@@ -0,0 +1,36 @@
+// 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
+
+import Core library "io";
+
+import library "day4_common";
+import library "io_utils";
+
+fn Run() {
+  var search: Wordsearch = Wordsearch.Read();
+  var xmas: [i32; 4] = (0x58, 0x4D, 0x41, 0x53);
+  var found: i32 = 0;
+
+  // TODO: Use for loops once they're implemented.
+  var y: i32 = 0;
+  while (y < 140) {
+    var x: i32 = 0;
+    while (x < 140) {
+      var dy: i32 = -1;
+      while (dy <= 1) {
+        var dx: i32 = -1;
+        while (dx <= 1) {
+          if (search.Check4(xmas, x, y, dx, dy)) {
+            ++found;
+          }
+          ++dx;
+        }
+        ++dy;
+      }
+      ++x;
+    }
+    ++y;
+  }
+  Core.Print(found);
+}

examples/advent2024/day4_part2.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
+
+import Core library "io";
+
+import library "day4_common";
+import library "io_utils";
+
+fn Run() {
+  var search: Wordsearch = Wordsearch.Read();
+  var mas: [i32; 3] = (0x4D, 0x41, 0x53);
+  var found: i32 = 0;
+
+  // TODO: Use for loops once they're implemented.
+  var y: i32 = 1;
+  while (y < 139) {
+    var x: i32 = 1;
+    while (x < 139) {
+      if ((search.Check3(mas, x - 1, y - 1, 1, 1) or
+           search.Check3(mas, x + 1, y + 1, -1, -1)) and
+          (search.Check3(mas, x - 1, y + 1, 1, -1) or
+           search.Check3(mas, x + 1, y - 1, -1, 1))) {
+        ++found;
+      }
+      ++x;
+    }
+    ++y;
+  }
+  Core.Print(found);
+}