aoc2025/day2/day2a.zig

const std = @import("std");

const allocator = std.heap.page_allocator;

pub fn main() !void {
    var printBuf: [1024]u8 = undefined;

    const inputFile = try std.fs.cwd().openFile(
        "input.txt",
        .{
            .mode = .read_only,
        },
    );
    defer inputFile.close();

    var inputFileBuffer: [1024]u8 = undefined;
    var inputFileReader = inputFile.reader(&inputFileBuffer);
    const inputFileSize = try inputFileReader.getSize();

    const inputBuffer = try allocator.alloc(u8, inputFileSize);
    try inputFileReader.interface.readSliceAll(inputBuffer);

    var counter:u64 = 0;

    var it = std.mem.tokenizeAny(u8, inputBuffer, ",\n");
    while (it.next()) |token| {
        const dashPos = std.mem.indexOf(u8, token, "-").?;
        const startRangeText = token[0..dashPos];
        const endRangeText = token[dashPos+1..];

        const startRange = try std.fmt.parseInt(u64, startRangeText, 10);
        const endRange = try std.fmt.parseInt(u64, endRangeText, 10);

        for (startRange..endRange+1) |id| {
            const idText = try std.fmt.bufPrint(&printBuf, "{d}", .{id});
            const halfLen = idText.len/2;
            const firstHalfText = idText[0..halfLen];
            const secondHalfText = idText[halfLen..];
            if (std.mem.eql(u8, firstHalfText, secondHalfText)) {
                counter += id;
            }
        }
    }

    try std.fs.File.stdout().writeAll(
      try std.fmt.bufPrint(&printBuf, "{}\n", .{counter}));
}