Initial commit: Day 1

.gitignore

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+zig-cache/
+zig-out/

day1/build.zig

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+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/results

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+info: [Part 1] There were 1521 increases
+info: [Part 2] There were 1543 increases

day1/src/main.zig

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+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;
+
+    // Part 1
+    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 depths = std.ArrayList(u32).init(alloc);
+    defer depths.deinit();
+
+    var it = std.mem.tokenize(contents, "\n");
+    var max: u32 = 0;
+    var increases: u32 = 0;
+    while (it.next()) |line| {
+        var v = try std.fmt.parseInt(u32, line, 10);
+        // This will always happen
+        defer max = v;
+        // Fill in the depths for part2
+        try depths.append(v);
+        if (max == 0) {
+            continue;
+        }
+        if (v > max) {
+            increases += 1;
+        }
+    }
+    std.log.info("[Part 1] There were {} increases", .{increases});
+
+    // Part 2
+    // Working with a sliding window of 3
+    var i: usize = 0;
+    increases = 0;
+    max = 0;
+    while (i < depths.items.len - 3) : (i += 1) {
+        // Current window
+        var a: u32 = depths.items[i] + depths.items[i+1] + depths.items[i+2];
+        var b: u32 = depths.items[i+1] + depths.items[i+2] + depths.items[i+3];
+        // Visualize it
+        //std.log.info("A: {} // B: {}\n{} A\n{} A B\n{} A B\n{}   B\n",
+        //             .{a, b, depths.items[i], depths.items[i+1],
+        //               depths.items[i+2], depths.items[i+3]});
+        if (b > a) {
+            increases += 1;
+        }
+    }
+    std.log.info("[Part 2] There were {} increases", .{increases});
+}