Finish day 2

day2/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("day2", "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);
+}

day2/result

@@ -0,0 +1,2 @@
+info: [Part 1] Depth 916, Horizontal Position 1845, Sum 1690020
+info: [Part 2] Depth 763408, Horizontal Position 1845, Sum 1408487760

day2/src/main.zig

@@ -0,0 +1,58 @@
+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);
+
+    // Part 1
+    var pos_x: i32 = 0;
+    var depth: i32 = 0;
+
+    var it = std.mem.tokenize(contents, "\n");
+    while (it.next()) |line| {
+        var lit = std.mem.tokenize(line, " ");
+        var dir = lit.next().?;
+        var amount = try std.fmt.parseInt(i32, lit.next().?, 10);
+        if (std.mem.eql(u8, dir, "up")) {
+            depth -= amount;
+        }
+        else if (std.mem.eql(u8, dir, "forward")) {
+            pos_x += amount;
+        }
+        else if (std.mem.eql(u8, dir, "down")) {
+            depth += amount;
+        }
+    }
+    std.log.info("[Part 1] Depth {}, Horizontal Position {}, Sum {}",
+                 .{depth, pos_x, depth * pos_x});
+
+    // Part 2
+    pos_x = 0;
+    var aim: i32 = 0;
+    depth = 0;
+    it = std.mem.tokenize(contents, "\n");
+    while (it.next()) |line| {
+        var lit = std.mem.tokenize(line, " ");
+        var dir = lit.next().?;
+        var amount = try std.fmt.parseInt(i32, lit.next().?, 10);
+        if (std.mem.eql(u8, dir, "up")) {
+            aim -= amount;
+        }
+        else if (std.mem.eql(u8, dir, "forward")) {
+            depth += amount * aim;
+            pos_x += amount;
+        }
+        else if (std.mem.eql(u8, dir, "down")) {
+            aim += amount;
+        }
+    }
+    std.log.info("[Part 2] Depth {}, Horizontal Position {}, Sum {}",
+                 .{depth, pos_x, depth * pos_x});
+}