solve day 1

.gitignore

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+zig-cache
+zig-out

build.zig

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+const std = @import("std");
+
+// Although this function looks imperative, note that its job is to
+// declaratively construct a build graph that will be executed by an external
+// runner.
+pub fn build(b: *std.Build) void {
+    // Standard target options allows the person running `zig build` to choose
+    // what target to build for. Here we do not override the defaults, which
+    // means any target is allowed, and the default is native. Other options
+    // for restricting supported target set are available.
+    const target = b.standardTargetOptions(.{});
+
+    // Standard optimization options allow the person running `zig build` to select
+    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
+    // set a preferred release mode, allowing the user to decide how to optimize.
+    const optimize = b.standardOptimizeOption(.{});
+
+    const exe = b.addExecutable(.{
+        .name = "advent-of-code-2023",
+        // In this case the main source file is merely a path, however, in more
+        // complicated build scripts, this could be a generated file.
+        .root_source_file = .{ .path = "src/main.zig" },
+        .target = target,
+        .optimize = optimize,
+    });
+
+    // This declares intent for the executable to be installed into the
+    // standard location when the user invokes the "install" step (the default
+    // step when running `zig build`).
+    b.installArtifact(exe);
+
+    // This *creates* a Run step in the build graph, to be executed when another
+    // step is evaluated that depends on it. The next line below will establish
+    // such a dependency.
+    const run_cmd = b.addRunArtifact(exe);
+
+    // By making the run step depend on the install step, it will be run from the
+    // installation directory rather than directly from within the cache directory.
+    // This is not necessary, however, if the application depends on other installed
+    // files, this ensures they will be present and in the expected location.
+    run_cmd.step.dependOn(b.getInstallStep());
+
+    // This allows the user to pass arguments to the application in the build
+    // command itself, like this: `zig build run -- arg1 arg2 etc`
+    if (b.args) |args| {
+        run_cmd.addArgs(args);
+    }
+
+    // This creates a build step. It will be visible in the `zig build --help` menu,
+    // and can be selected like this: `zig build run`
+    // This will evaluate the `run` step rather than the default, which is "install".
+    const run_step = b.step("run", "Run the app");
+    run_step.dependOn(&run_cmd.step);
+
+    // Creates a step for unit testing. This only builds the test executable
+    // but does not run it.
+    const unit_tests = b.addTest(.{
+        .root_source_file = .{ .path = "src/main.zig" },
+        .target = target,
+        .optimize = optimize,
+    });
+
+    const run_tests = b.addRunArtifact(unit_tests);
+
+    // Similar to creating the run step earlier, this exposes a `test` step to
+    // the `zig build --help` menu, providing a way for the user to request
+    // running the unit tests.
+    const test_step = b.step("test", "Run unit tests");
+    test_step.dependOn(&run_tests.step);
+}

src/day1.zig

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+const std = @import("std");
+
+const StringArray = std.ArrayList([]const u8);
+const digits = [_][]const u8{ "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" };
+
+pub fn part1(lines: [][]const u8) u32 {
+    var sum: u32 = 0;
+    for (lines) |line| {
+        var first_digit: u8 = 0;
+        var last_digit: u8 = 0;
+
+        for (line) |c| {
+            if (!std.ascii.isDigit(c)) continue;
+
+            if (first_digit == 0) {
+                first_digit = c - '0';
+                last_digit = first_digit;
+            } else {
+                last_digit = c - '0';
+            }
+        }
+
+        var number = 10*first_digit + last_digit;
+        sum += number;
+    }
+
+    return sum;
+}
+
+pub fn part2(lines: [][]const u8) u32 {
+    var sum: u32 = 0;
+    for (lines) |line| {
+        var first_digit: u8 = 0;
+        {
+            var found_first = false;
+            var first_idx: usize = 0;
+            for (0.., line) |i, c| {
+                if (!std.ascii.isDigit(c)) continue;
+
+                first_digit = c - '0';
+                first_idx = i;
+                found_first = true;
+                break;
+            }
+
+            for (0.., digits) |i, digit| {
+                var occurence_opt = std.mem.indexOf(u8, line, digit);
+                if (occurence_opt == null) continue;
+                var occurence = occurence_opt.?;
+
+                if (found_first and occurence > first_idx) continue;
+
+                first_digit = @intCast(i);
+                found_first = true;
+                first_idx = occurence;
+            }
+        }
+
+        var last_digit: u8 = 0;
+        {
+            var found_last = false;
+            var last_idx: usize = 0;
+            for (0.., line) |i, c| {
+                if (!std.ascii.isDigit(c)) continue;
+
+                last_digit = c - '0';
+                last_idx = i;
+                found_last = true;
+            }
+
+            for (0.., digits) |i, digit| {
+                var occurence_opt = std.mem.lastIndexOf(u8, line, digit);
+                if (occurence_opt == null) continue;
+                var occurence = occurence_opt.?;
+
+                if (found_last and occurence < last_idx) continue;
+
+                last_digit = @intCast(i);
+                found_last = true;
+                last_idx = occurence;
+            }
+        }
+
+        var number = 10*first_digit + last_digit;
+        sum += number;
+    }
+
+    return sum;
+}
+
+test "part 1 example" {
+    var input = [_][]const u8{
+        "1abc2",
+        "pqr3stu8vwx",
+        "a1b2c3d4e5f",
+        "treb7uchet",
+    };
+    var actual = part1(&input);
+    var expected: u32 = 142;
+    try std.testing.expectEqual(expected, actual);
+}
+
+test "part 2 example" {
+    var input = [_][]const u8{
+        "two1nine",
+        "eightwothree",
+        "abcone2threexyz",
+        "xtwone3four",
+        "4nineeightseven2",
+        "zoneight234",
+        "7pqrstsixteen",
+    };
+    var actual = part2(&input);
+    var expected: u32 = 281;
+    try std.testing.expectEqual(expected, actual);
+}

src/main.zig

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+const std = @import("std");
+const StringArray = std.ArrayList([]const u8);
+
+const Day1 = @import("./day1.zig");
+
+pub fn main() !void {
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    const allocator = gpa.allocator();
+    defer {
+        if (gpa.deinit() == .leak) @panic("Leaked memory");
+    }
+
+    var file = try std.fs.cwd().openFile("input.txt", .{});
+    defer file.close();
+
+    var buf_reader = std.io.bufferedReader(file.reader());
+    var reader = buf_reader.reader();
+
+    var lines = StringArray.init(allocator);
+    defer {
+        for (lines.items) |line| {
+            allocator.free(line);
+        }
+        lines.deinit();
+    }
+
+    var line_buf: [1024]u8 = undefined;
+    while (try reader.readUntilDelimiterOrEof(&line_buf, '\n')) |line| {
+        var trimmed_line = std.mem.trimRight(u8, line, &.{'\r'});
+        try lines.append(try allocator.dupe(u8, trimmed_line));
+    }
+
+    std.debug.print("day1: {d}\n", .{Day1.part1(lines.items)});
+    std.debug.print("day2: {d}\n", .{Day1.part2(lines.items)});
+}