4s to run part 2. But still happy with it.
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9ffad3b1b4
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8ea740f029
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AB49BD6B2B3A6377
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const std = @import("std");
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const Dir = enum(usize) { up, right, down, left };
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const Coord = struct { row: usize, col: usize };
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const Beam = struct { dir: Dir, coord: Coord };
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pub fn main() !void {
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var content = @embedFile("data.txt");
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var gpa = std.heap.GeneralPurposeAllocator(.{}){};
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const allocator = gpa.allocator();
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var grid = std.ArrayList(std.ArrayList(u8)).init(allocator);
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defer grid.deinit();
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var lines = std.mem.split(u8, content, "\n");
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while (lines.next()) |line| {
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if (line.len < 1) {
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break;
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}
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var lineArrayList = std.ArrayList(u8).init(allocator);
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for (line) |char| {
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try lineArrayList.append(char);
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}
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try grid.append(lineArrayList);
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}
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const energy = try energize(Beam{ .dir = Dir.right, .coord = Coord{ .row = 0, .col = 0 } }, grid);
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std.debug.print("Part 1: {d}\n", .{energy});
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const height = grid.items.len;
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const width = grid.items[0].items.len;
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var maxEnergy: usize = 0;
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for (0..height) |row| {
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for ([_]usize{ 0, width - 1 }) |col| {
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const dir = if (col == 0) Dir.right else Dir.left;
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const start = Beam{ .dir = dir, .coord = Coord{ .row = row, .col = col } };
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const e = try energize(start, grid);
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if (e > maxEnergy) {
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maxEnergy = e;
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}
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}
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}
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for (0..width) |col| {
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for ([_]usize{ 0, height - 1 }) |row| {
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const dir = if (row == 0) Dir.down else Dir.up;
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const start = Beam{ .dir = dir, .coord = Coord{ .row = row, .col = col } };
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const e = try energize(start, grid);
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if (e > maxEnergy) {
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maxEnergy = e;
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}
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}
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}
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std.debug.print("Part 2: {d}\n", .{maxEnergy});
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}
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fn energize(start: Beam, grid: std.ArrayList(std.ArrayList(u8))) !usize {
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var gpa = std.heap.GeneralPurposeAllocator(.{}){};
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const allocator = gpa.allocator();
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var beams = std.ArrayList(Beam).init(allocator);
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defer beams.deinit();
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// add the first beam
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try beams.append(start);
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var energized = std.AutoHashMap(Coord, void).init(allocator);
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defer energized.deinit();
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var beamHistory = std.AutoHashMap(Beam, void).init(allocator);
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defer beamHistory.deinit();
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const height = grid.items.len;
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const width = grid.items[0].items.len;
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while (true) {
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// make 2 new lists: beams to add, and beams to remove.
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// batch these while iterating, and do it all after
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var beamsToAdd = std.ArrayList(Beam).init(allocator);
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defer beamsToAdd.deinit();
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var beamsToRemove = std.ArrayList(usize).init(allocator);
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defer beamsToRemove.deinit();
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if (beams.items.len == 0) {
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break;
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}
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for ((&beams).items, 0..) |*b, beamNumber| {
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if (isOutOfGrid(b, grid)) {
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try beamsToRemove.append(beamNumber);
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continue;
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}
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try energized.put(b.coord, {});
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if (beamHistory.contains(b.*)) {
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try beamsToRemove.append(beamNumber);
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continue;
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}
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try beamHistory.put(b.*, {});
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const row = b.coord.row;
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const col = b.coord.col;
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const value = grid.items[row].items[col];
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const goStraight = value == '.' or (value == '|' and (b.dir == .up or b.dir == .down)) or
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(value == '-' and (b.dir == .left or b.dir == .right));
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if (goStraight) {
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switch (b.dir) {
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.up => if (row == 0) {
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b.coord.row = height + 10; // put it out of the grid to get cleaned up
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} else {
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b.coord.row -= 1;
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},
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.right => b.coord.col += 1,
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.down => b.coord.row += 1,
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.left => if (col == 0) {
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b.coord.col = width + 10; // put it out of the grid to get cleaned up
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} else {
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b.coord.col -= 1;
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},
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}
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} else if (value == '|') {
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if (row == 0) {
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// if we are on the top row, change the beam to go down
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b.dir = Dir.down;
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b.coord.row += 1;
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} else {
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// otherwise, change beam direction to up and move it up one cell
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b.dir = Dir.up;
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b.coord.row -= 1;
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if (row != height - 1) {
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// and if we're not on the _bottom_ row,
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// create a new beam going down, below this cell
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const newBeam = Beam{ .dir = Dir.down, .coord = Coord{ .row = row + 1, .col = col } };
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try beamsToAdd.append(newBeam);
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}
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}
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} else if (value == '-') {
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if (col == 0) {
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// if we are on the first col, change the beam to go right
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b.dir = Dir.right;
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b.coord.col += 1;
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} else {
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// otherwise, change beam direction to left and move it left one cell
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b.dir = Dir.left;
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b.coord.col -= 1;
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if (col != width - 1) {
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// and if we're not on the _last_ column,
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// create a new beam going right, to the right this cell
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const newBeam = Beam{ .dir = Dir.right, .coord = Coord{ .row = row, .col = col + 1 } };
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try beamsToAdd.append(newBeam);
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}
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}
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} else if (value == '/') {
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switch (b.dir) {
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.up => {
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b.dir = Dir.right;
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b.coord.col += 1;
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},
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.right => if (row == 0) {
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b.coord.row = height + 10; // put it out of the grid to get cleaned up
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} else {
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b.dir = Dir.up;
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b.coord.row -= 1;
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},
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.down => if (col == 0) {
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b.coord.row = height + 10; // put it out of the grid to get cleaned up
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} else {
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b.dir = Dir.left;
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b.coord.col -= 1;
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},
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.left => {
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b.dir = Dir.down;
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b.coord.row += 1;
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},
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}
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} else if (value == '\\') {
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switch (b.dir) {
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.up => if (col == 0) {
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b.coord.col = width + 10; // put it out of the grid to get cleaned up
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} else {
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b.dir = Dir.left;
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b.coord.col -= 1;
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},
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.right => {
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b.dir = Dir.down;
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b.coord.row += 1;
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},
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.down => {
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b.dir = Dir.right;
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b.coord.col += 1;
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},
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.left => if (row == 0) {
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b.coord.row = height + 10; // put it out of the grid to get cleaned up
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} else {
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b.dir = Dir.up;
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b.coord.row -= 1;
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},
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}
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}
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}
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// remove the beams in reverse order
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const len = beamsToRemove.items.len;
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for (0..len) |j| {
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const idx = beamsToRemove.items[len - j - 1];
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_ = beams.orderedRemove(idx);
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}
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beamsToRemove.clearAndFree();
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// add the new beams
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for (beamsToAdd.items) |beam| {
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try beams.append(beam);
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}
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beamsToAdd.clearAndFree();
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}
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return energized.count();
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}
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fn isOutOfGrid(beam: *Beam, grid: std.ArrayList(std.ArrayList(u8))) bool {
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const row = beam.coord.row;
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const col = beam.coord.col;
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const height = grid.items.len;
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const width = grid.items[0].items.len;
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return row < 0 or row >= height or col < 0 or col >= width;
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}
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fn printGrid(grid: std.ArrayList(std.ArrayList(u8)), energized: std.AutoHashMap(Coord, void)) void {
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for (grid.items, 0..) |line, row| {
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for (line.items, 0..) |char, col| {
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if (char == '.' and energized.contains(Coord{ .row = row, .col = col })) {
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std.debug.print("#", .{});
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} else {
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std.debug.print("{c}", .{char});
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}
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}
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std.debug.print("\n", .{});
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}
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}
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