AdventOfCode-2023/day08-easy/src/main.zig

const std = @import("std");

fn StackList(comptime T: type, comptime capacity_type: type, comptime capacity: capacity_type) type {
    return struct {
        const Self = @This();
        mem: [capacity]T,
        length: capacity_type,

        fn add(self: *Self, value: T) void {
            self.mem[self.length] = value;
            self.length += 1;
        }

        fn has(self: *const Self, needle: T) bool {
            for (0..self.length) |i| {
                if (self.mem[i] == needle) {
                    return true;
                }
            }

            return false;
        }

        fn getSlice(self: *Self) []T {
            //var mem_full_slice = &self.mem;
            //var mem_slice: []T = mem_full_slice[0..self.length];
            //return mem_slice;
            return (&self.mem)[0..self.length];
        }

        fn getLoopedValue(self: *const Self, index: usize) T {
            return self.mem[index % self.length];
        }

        fn reset(self: *Self) void {
            self.length = 0;
        }

        fn init() Self {
            return Self{
                .mem = undefined,
                .length = 0,
            };
        }
    };
}

const SIXTEEN_BITS = 65535;

const Directions = StackList(usize, usize, 1000);

fn parseDirections(line: []const u8) Directions {
    var result = Directions.init();

    const left: usize = SIXTEEN_BITS << 16;
    const right: usize = SIXTEEN_BITS;

    var index: usize = 0;
    while (index < line.len) : (index += 1) {
        result.add(switch (line[index]) {
            'L' => left,
            'R' => right,
            else => unreachable,
        });
    }

    return result;
}

const Nodes = [26 * 26 * 26]usize;

fn parseNodeNumber(line: []const u8) usize {
    var result: usize = 0;
    for (line) |char| {
        result = (result * 26) + (char - 'A');
    }

    return result;
}

fn parseNodeLine(line: []const u8, state: *Nodes) usize {
    const current_node_number = parseNodeNumber(line[0..3]);
    state[current_node_number] = (parseNodeNumber(line[7..10]) << 16) | parseNodeNumber(line[12..15]);
    return current_node_number;
}

fn solve(nodes: Nodes, directions: Directions, start: usize, end: usize) usize {
    var current = start;
    var i: usize = 0;
    while (current != end) : (i += 1) {
        const mask = nodes[current] & directions.getLoopedValue(i);
        current = (mask | (mask >> 16)) & SIXTEEN_BITS;

        //if (i % directions.length == 0) {
        //std.debug.print("Iteration {d}; current: {d}\n", .{ i, current });
        //}
    }

    return i;
}

pub fn main() !void {
    const stdout = std.io.getStdOut().writer();

    const raw_in = std.io.getStdIn();
    var buffered_reader = std.io.bufferedReader(raw_in.reader());
    var reader = buffered_reader.reader();

    var line_buffer: [1000]u8 = undefined;
    const first_line = (try reader.readUntilDelimiterOrEof(&line_buffer, '\n')).?;
    var directions = parseDirections(first_line);
    _ = try reader.readUntilDelimiterOrEof(&line_buffer, '\n');

    var nodes: Nodes = undefined;
    for (&nodes) |*node| {
        node.* = (SIXTEEN_BITS << 16) | SIXTEEN_BITS;
    }
    const third_line = (try reader.readUntilDelimiterOrEof(&line_buffer, '\n')).?;
    const start = parseNodeLine(third_line, &nodes);
    _ = start;
    var end: usize = 0;
    while (try reader.readUntilDelimiterOrEof(&line_buffer, '\n')) |line| {
        end = parseNodeLine(line, &nodes);
    }

    const result = solve(nodes, directions, 0, nodes.len - 1);
    try stdout.print("{d}\n", .{result});
}