1 files changed, 52 insertions, 0 deletions
diff --git a/src/05/main.zig b/src/05/main.zig
new file mode 100644
index 0000000..30f491f
--- /dev/null
+++ b/src/05/main.zig
@@ -0,0 +1,52 @@
+const std = @import("std");
+const aoc = @import("aoc");
+
+const row_count = 128;
+const col_count = 8;
+
+// Input is coded in a way that we can do an implicit binary search by replacing
+// identifiers for the lower half with "0" and for the upper half with "1"
+// See commit <f1b717029cf3262c1fa2760124af258924d668da> for actual binary search
+
+fn code2Id(input: []const u8) !u32 {
+    var value: u32 = 0;
+    for (input) |c|
+        value = value * 2 + @boolToInt(c == 'B' or c == 'R');
+    return value;
+}
+
+fn part1(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
+    _ = args;
+
+    var lineit = std.mem.tokenize(u8, input, "\n");
+    var answer: u32 = 0;
+    while (lineit.next()) |line| {
+        const id = try code2Id(line[0..10]);
+        answer = std.math.max(answer, id);
+    }
+
+    return try std.fmt.allocPrint(allocator, "{d}", .{answer});
+}
+
+fn part2(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
+    _ = args;
+
+    var lineit = std.mem.tokenize(u8, input, "\n");
+    var seats = [_]u1{0} ** (row_count * col_count);
+    var min: u32 = std.math.inf_u32;
+    while (lineit.next()) |line| {
+        const id = try code2Id(line);
+        min = std.math.min(min, id);
+        seats[id] = 1;
+    }
+
+    for (seats[min..]) |_, i| {
+        if (seats[min + i] == 0) {
+            return try std.fmt.allocPrint(allocator, "{d}", .{min + i});
+        }
+    }
+
+    return null;
+}
+
+pub const main = aoc.main(part1, part2, .{ "850", "599" });