1 files changed, 19 insertions, 0 deletions
diff --git a/aoc/2021/03/part-one.zig b/aoc/2021/03/part-one.zig
new file mode 100644
index 0000000..6088925
--- /dev/null
+++ b/aoc/2021/03/part-one.zig
@@ -0,0 +1,19 @@
+const print = @import("std").debug.print;
+
+const input = @embedFile("input");
+const mean = @splat(12, @as(u16, '0' * 1000 + 500));
+const pos = @Vector(12, u4){ 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 };
+
+pub fn main() !void {
+    var sum = @splat(12, @as(u16, 0));
+    var i = @as(usize, 0);
+    while (i < input.len) : (i += 13) {
+        var j = @as(usize, 0);
+        while (j < 12) : (j += 1)
+            sum[j] += input[i + j];
+    }
+
+    const common = @bitCast(@Vector(12, u1), sum > mean);
+    const gamma = @reduce(.Add, @as(@Vector(12, u12), common) << pos);
+    print("{}\n", .{ @as(usize, gamma) * ~gamma });
+}