aoc2022/01/2.zig

const std = @import("std");

// NOTE: I know this is way too overengineered, but I wanted
//       to make it as efficient as possible.

pub fn main() !void {
    const input = @embedFile("input");

    // Putting part 1's solution as an extra :P
    std.debug.print("Part 1's solution: {}\n", .{sumTopNElves(input, 1)});
    std.debug.print("Part 2's solution: {}\n", .{sumTopNElves(input, 3)});
}

// Returns the sum of the <cant> elves with the most calories from <string>
pub fn sumTopNElves(input: []const u8, comptime cant: usize) usize {
    var iter = ElfIterator.init(input);
    // Initialize the buffer where the 3 numbers will lie
    var maxArr: [cant]usize = .{0} ** cant;
    // Keeps track of which is the smallest index of the array
    var min_i: usize = 0;

    // Iterate through each elf's sum of calories as usize
    while (iter.next()) |elf| {
        // Check if the current elf carries more
        // calories than the previous smallest max
        if (elf > maxArr[min_i]) {
            maxArr[min_i] = elf;

            // maxArr changed, update what is the smallest index
            var advance: usize = 1;
            while (advance < cant) : (advance += 1) {
                // Advance and wrap around
                const i = (min_i + advance) % cant;

                if (maxArr[i] < maxArr[min_i]) min_i = i;
            }
        }
    }

    var res: usize = 0;
    inline for (maxArr) |num| {
        res += num;
    }

    return res;
}

// Helper to return the total of calories per elf one at a time
const ElfIterator = struct {
    iter: std.mem.SplitIterator(u8),

    pub fn init(input: []const u8) ElfIterator {
        return ElfIterator{
            // We assume the input file is properly formatted
            .iter = std.mem.split(u8, input, "\n"),
        };
    }

    pub fn next(self: *ElfIterator) ?usize {
        var res: usize = 0;

        while (self.iter.next()) |calories| {
            // If non numeric assume EOF (End Of elF)
            res += std.fmt.parseInt(usize, calories, 10) catch return res;
        }

        // If we reach EOF (End Of File, do not confuse with End Of elF), return null
        return null;
    }
};