day 4

day4_p1.zig

@@ -0,0 +1,36 @@
+// Hey puzzle designer, why ????
+const std = @import("std");
+
+pub fn main() !void {
+    const stdin = std.io.getStdIn();
+    var buf_io = std.io.bufferedReader(stdin.reader());
+    var reader = buf_io.reader();
+
+    var buf = [_]u8{0} ** 100;
+    _ = try reader.readAll(&buf);
+
+    const stripped = std.mem.trim(u8, &buf, " \n\r\x00");
+    const solution = try mine(stripped);
+    std.debug.print("{d}", .{solution});
+}
+
+fn mine(key: []const u8) !u64 {
+    var buf = [_]u8{0} ** 10000;
+    for (1..1e10) |i| {
+        const candidate = try std.fmt.bufPrintZ(&buf, "{s}{d}", .{ key, i });
+        var result = [_]u8{0} ** std.crypto.hash.Md5.digest_length;
+        std.crypto.hash.Md5.hash(candidate, &result, .{});
+
+        // Check first 5 zeroes (2 bytes and.. a half)
+        if (result[0] == 0 and result[1] == 0 and result[2] < 0x10) {
+            return i;
+        }
+    }
+
+    return 0;
+}
+
+test "day-test" {
+    try std.testing.expectEqual(try mine("abcdef"), 609043);
+    try std.testing.expectEqual(try mine("pqrstuv"), 1048970);
+}

day4_p2.zig

@@ -0,0 +1,31 @@
+// Hey puzzle designer, why ????
+const std = @import("std");
+
+pub fn main() !void {
+    const stdin = std.io.getStdIn();
+    var buf_io = std.io.bufferedReader(stdin.reader());
+    var reader = buf_io.reader();
+
+    var buf = [_]u8{0} ** 100;
+    _ = try reader.readAll(&buf);
+
+    const stripped = std.mem.trim(u8, &buf, " \n\r\x00");
+    const solution = try mine(stripped);
+    std.debug.print("{d}", .{solution});
+}
+
+fn mine(key: []const u8) !u64 {
+    var buf = [_]u8{0} ** 10000;
+    for (1..1e10) |i| {
+        const candidate = try std.fmt.bufPrintZ(&buf, "{s}{d}", .{ key, i });
+        var result = [_]u8{0} ** std.crypto.hash.Md5.digest_length;
+        std.crypto.hash.Md5.hash(candidate, &result, .{});
+
+        // Check first 6 zeroes (3 bytes)
+        if (result[0] == 0 and result[1] == 0 and result[2] == 0) {
+            return i;
+        }
+    }
+
+    return 0;
+}