add day 5

1 files changed, 63 insertions, 0 deletions

diff --git a/day_03.zig b/day_03.zig
new file mode 100644
index 0000000..b33c5cf
--- /dev/null
+++ b/day_03.zig
@@ -0,0 +1,63 @@
+const std = @import("std");
+const Result = @import("util/aoc.zig").Result;
+
+pub fn puzzle_1(input: []const u8) Result {
+    var iter = std.mem.split(u8, input, "\n");
+
+    var count: u16 = 0;
+    while (iter.next()) |line| {
+        var p1: u64 = 0;
+        var p2: u64 = 0;
+
+        // A note to whoever reads this in the future
+        // A to Z -> 65 to 90
+        // a to z -> 97 to 122
+        //
+        // u64 is ok
+        // 90 - 65 + 122 - 97 = 50
+
+        for (line[0 .. line.len / 2]) |_, i| {
+            p1 |= @as(u64, 1) << @intCast(u6, line[i] - 65); // 65 == 'A'
+            p2 |= @as(u64, 1) << @intCast(u6, line[i + line.len / 2] - 65);
+        }
+
+        // Example
+        //
+        // p1: 0000000101100010001000110000000000011000000011000010000100
+        // p2: 1000001000000000000110000000000000000001011001100001100000
+        //
+        //  &: 0000000000000000000000000000000000000000000001000000000000 = 46 0s
+        //
+        //  65 + 63 - 46 = 82 = R
+
+        count += char_to_priority(@intCast(u8, 65 + 63) - @clz(p1 & p2));
+    }
+
+    return .{ .int = count };
+}
+
+pub fn puzzle_2(input: []const u8) Result {
+    var iter = std.mem.split(u8, input, "\n");
+
+    var count: u16 = 0;
+    mainLoop: while (true) {
+        var parts = std.mem.zeroes([3]u64);
+
+        for (parts) |*p| {
+            const line = iter.next() orelse break :mainLoop;
+            for (line) |_, i| {
+                p.* |= @as(u64, 1) << @intCast(u6, line[i] - 65);
+            }
+        }
+
+        count += char_to_priority(@intCast(u8, 65 + 63) - @clz(parts[0] & parts[1] & parts[2]));
+    }
+
+    return .{ .int = count };
+}
+
+fn char_to_priority(char: u8) u8 {
+    if (char >= 65 and char <= 90)
+        return char - 38;
+    return char - 96;
+}