aoc2025/day3/day3a.zig

const std = @import("std");

const allocator = std.heap.page_allocator;



fn findLargestDigitPos(batteryLine: []const u8) usize {
    var largestPos: usize = 0;
    var largestDigit: u8 = 0;

    for (batteryLine, 0..) |digit, pos| {
        if (digit > largestDigit) {
            largestDigit = digit;
            largestPos = pos;
        }
    }

    return largestPos;
}

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.tokenizeScalar(u8, inputBuffer, '\n');
    while (it.next()) |batteryLine| {
        const largestPos = findLargestDigitPos(batteryLine[0..batteryLine.len-1]);
        const secondLargestPos = findLargestDigitPos(batteryLine[largestPos+1..]) + largestPos + 1;

        counter += @intCast((batteryLine[largestPos] - '0') * 10 +
                            (batteryLine[secondLargestPos] - '0'));
    }

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