advent-of-code-2023/day3/main.zig

const std = @import("std");
const lib = @import("lib.zig");

const Number = struct { row: usize, col: usize, length: usize, value: u32 };

pub fn main() !void {
    const content = @embedFile("data.txt");
    const grid = try lib.splitArrayIntoArrayList(content, "\n");
    defer grid.deinit();

    const numbers = try parseNumbers(grid);
    defer numbers.deinit();

    var total1: u128 = 0;

    for (numbers.items) |n| {
        if (numberTouchesSymbol(n, grid)) {
            total1 += n.value;
        }
    }

    std.debug.print("total1 {d}\n", .{total1});

    var total2: u128 = 0;
    for (grid.items, 0..) |line, row| {
        for (line, 0..) |val, col| {
            if (val == '*') {
                total2 += try findGearRatio(row, col, numbers);
            }
        }
    }
    std.debug.print("total2 {d}\n", .{total2});
}

fn findGearRatio(row: usize, col: usize, numbers: std.ArrayList(Number)) !u32 {
    const touching = try findNumbersTouchingCell(row, col, numbers);
    if (touching.items.len != 2) {
        return 0;
    }
    return touching.items[0].value * touching.items[1].value;
}

fn findNumbersTouchingCell(row: usize, col: usize, numbers: std.ArrayList(Number)) !std.ArrayList(Number) {
    const allocator = std.heap.page_allocator;
    var touching = std.ArrayList(Number).init(allocator);

    for (numbers.items) |n| {
        // itreate over each digit in the number
        for (0..n.length) |i| {
            // TODO: upgrade to Zig .12 to get @abs
            // if (@abs(n.row - row) < 1 and @abs(n.col + i - col) < 1) {
            if ((n.row == row or n.row + 1 == row or n.row == row + 1) and (n.col + i == col or n.col + 1 + i == col or n.col + i == col + 1)) {
                try touching.append(n);
                break;
            }
        }
    }
    return touching;
}

fn numberTouchesSymbol(n: Number, grid: std.ArrayList([]const u8)) bool {
    const items = grid.items;
    const width = items[0].len;
    const height = items.len - 1; // TODO: fix extra crap when i read files..

    // itreate over each digit in the number
    for (0..n.length) |i| {
        // over the 3 nearest rows
        for (0..3) |r| {
            // and the 3 nearest columns
            for (0..3) |c| {
                const outOfBounds = (r == 0 and n.row == 0) or (c == 0 and n.col + i == 0) or (r == 2 and n.row + 1 == height) or (c == 2 and n.col + i + 1 == width);

                if (!outOfBounds) {
                    const row = n.row + r - 1;
                    const col = n.col + c + i - 1;
                    const val = items[row][col];
                    if (!std.ascii.isDigit(val) and val != '.') {
                        return true;
                    }
                }
            }
        }
    }
    return false;
}

fn parseNumbers(grid: std.ArrayList([]const u8)) !std.ArrayList(Number) {
    const allocator = std.heap.page_allocator;
    var numbers = std.ArrayList(Number).init(allocator);

    for (grid.items, 0..) |line, row| {
        var numList = std.ArrayList(u8).init(allocator);
        defer numList.deinit();

        for (line, 0..) |val, col| {
            if (std.ascii.isDigit(val)) {
                try numList.append(val);
            }

            // if we have a number started, and we've encountered a non-digit (or the end of the grid)
            if (numList.items.len != 0 and (!std.ascii.isDigit(val) or col == line.len - 1)) {
                const parsed = try std.fmt.parseInt(u32, numList.items, 10);
                const length = numList.items.len;
                try numbers.append(Number{ .row = row, .col = col - length, .length = length, .value = parsed });
                numList.items.len = 0;
            }
        }
    }

    return numbers;
}