Add zig implementation of day 1

.gitignore

@@ -1 +1,3 @@
 bin/
+zig-out/
+zig-cache/

day1/build.zig

@@ -0,0 +1,27 @@
+const std = @import("std");
+
+pub fn build(b: *std.build.Builder) 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 release options allow the person running `zig build` to select
+    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall.
+    const mode = b.standardReleaseOptions();
+
+    const exe = b.addExecutable("day1", "src/main.zig");
+    exe.setTarget(target);
+    exe.setBuildMode(mode);
+    exe.install();
+
+    const run_cmd = exe.run();
+    run_cmd.step.dependOn(b.getInstallStep());
+    if (b.args) |args| {
+        run_cmd.addArgs(args);
+    }
+
+    const run_step = b.step("run", "Run the app");
+    run_step.dependOn(&run_cmd.step);
+}

day1/src/main.zig

@@ -0,0 +1,36 @@
+const std = @import("std");
+
+pub fn main() anyerror!void {
+    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+    defer arena.deinit();
+    const alloc = &arena.allocator;
+
+    // Read our input
+    var f = try std.fs.cwd().openFile("input", .{});
+    defer f.close();
+    var contents = try f.readToEndAlloc(alloc, std.math.maxInt(u32));
+    defer alloc.free(contents);
+
+    var it = std.mem.tokenize(contents, "\n");
+    var sum: u64 = 0;
+    var sum2: u64 = 0;
+    while (it.next()) |v| {
+        var val: u64 = try std.fmt.parseInt(u64, v, 10);
+        val /= 3;
+        val -= 2;
+        sum += val;
+        sum2 += val;
+        while (val > 0) {
+            val /= 3;
+            if (val < 2) {
+                val = 0;
+            }
+            else {
+                val -= 2;
+            }
+            sum2 += val;
+        }
+    }
+    std.log.info("[Part 1] Sum: {}", .{sum});
+    std.log.info("[Part 2] Sum: {}", .{sum2});
+}