aoc2022/08/1-2.zig

const std = @import("std");

// This one isn't as commented. Sorry for that.

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

    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    defer arena.deinit();
    const allocator = arena.allocator();

    var iter = std.mem.split(u8, input[0 .. input.len - 1], "\n");
    const grid = iterCollapse([]const u8, &iter, allocator) catch unreachable;

    var nVisible: usize = 0;
    var bestPoints: usize = 0;

    // For each cell in the grid
    for (grid) |row, y| {
        for (row) |cell, x| {
            var cellVisible: bool = false;
            var cellPoints: usize = 1;
            defer {
                if (cellVisible) nVisible += 1;
                if (cellPoints > bestPoints) bestPoints = cellPoints;
            }

            // Look from the left
            var i: usize = x;
            var dirPoints: usize = 0;
            while (i > 0) : (i -= 1) {
                dirPoints += 1;
                if (grid[y][i - 1] >= cell) break;
            } else {
                cellVisible = true;
            }
            cellPoints *= dirPoints;

            // Look from the right
            i = x + 1;
            dirPoints = 0;
            while (i < grid[0].len) : (i += 1) {
                dirPoints += 1;
                if (grid[y][i] >= cell) break;
            } else {
                cellVisible = true;
            }
            cellPoints *= dirPoints;

            // Look from the top
            i = y;
            dirPoints = 0;
            while (i > 0) : (i -= 1) {
                dirPoints += 1;
                if (grid[i - 1][x] >= cell) break;
            } else {
                cellVisible = true;
            }
            cellPoints *= dirPoints;

            // Look from the bottom
            i = y + 1;
            dirPoints = 0;
            while (i < grid.len) : (i += 1) {
                dirPoints += 1;
                if (grid[i][x] >= cell) break;
            } else {
                cellVisible = true;
            }
            cellPoints *= dirPoints;
        }
    }

    print("Part 1: {}\n", .{nVisible});
    print("Part 2: {}\n", .{bestPoints});
}

// -------------------- UTIL --------------------

pub fn print(comptime fmt: []const u8, args: anytype) void {
    std.io.getStdOut().writer().print(fmt, args) catch unreachable;
}

pub fn iterCollapse(comptime T: type, iter: anytype, allocator: std.mem.Allocator) ![]T {
    var vector = std.ArrayList(T).init(allocator);

    if (!@hasDecl(@TypeOf(iter.*), "next")) {
        @compileError("Cannot collapse type " ++ @typeName(@TypeOf(iter.*)) ++ ". No .next() method.");
    }

    while (@field(iter.*, "next")()) |item| {
        try vector.append(item);
    }

    return vector.items;
}