4s to run part 2. But still happy with it.

master
Dustin Swan 6 months ago
parent 9ffad3b1b4
commit 8ea740f029
Signed by: dustinswan
GPG Key ID: AB49BD6B2B3A6377

@ -0,0 +1,254 @@
const std = @import("std");
const Dir = enum(usize) { up, right, down, left };
const Coord = struct { row: usize, col: usize };
const Beam = struct { dir: Dir, coord: Coord };
pub fn main() !void {
var content = @embedFile("data.txt");
var gpa = std.heap.GeneralPurposeAllocator(.{}){};
const allocator = gpa.allocator();
var grid = std.ArrayList(std.ArrayList(u8)).init(allocator);
defer grid.deinit();
var lines = std.mem.split(u8, content, "\n");
while (lines.next()) |line| {
if (line.len < 1) {
break;
}
var lineArrayList = std.ArrayList(u8).init(allocator);
for (line) |char| {
try lineArrayList.append(char);
}
try grid.append(lineArrayList);
}
const energy = try energize(Beam{ .dir = Dir.right, .coord = Coord{ .row = 0, .col = 0 } }, grid);
std.debug.print("Part 1: {d}\n", .{energy});
const height = grid.items.len;
const width = grid.items[0].items.len;
var maxEnergy: usize = 0;
for (0..height) |row| {
for ([_]usize{ 0, width - 1 }) |col| {
const dir = if (col == 0) Dir.right else Dir.left;
const start = Beam{ .dir = dir, .coord = Coord{ .row = row, .col = col } };
const e = try energize(start, grid);
if (e > maxEnergy) {
maxEnergy = e;
}
}
}
for (0..width) |col| {
for ([_]usize{ 0, height - 1 }) |row| {
const dir = if (row == 0) Dir.down else Dir.up;
const start = Beam{ .dir = dir, .coord = Coord{ .row = row, .col = col } };
const e = try energize(start, grid);
if (e > maxEnergy) {
maxEnergy = e;
}
}
}
std.debug.print("Part 2: {d}\n", .{maxEnergy});
}
fn energize(start: Beam, grid: std.ArrayList(std.ArrayList(u8))) !usize {
var gpa = std.heap.GeneralPurposeAllocator(.{}){};
const allocator = gpa.allocator();
var beams = std.ArrayList(Beam).init(allocator);
defer beams.deinit();
// add the first beam
try beams.append(start);
var energized = std.AutoHashMap(Coord, void).init(allocator);
defer energized.deinit();
var beamHistory = std.AutoHashMap(Beam, void).init(allocator);
defer beamHistory.deinit();
const height = grid.items.len;
const width = grid.items[0].items.len;
while (true) {
// make 2 new lists: beams to add, and beams to remove.
// batch these while iterating, and do it all after
var beamsToAdd = std.ArrayList(Beam).init(allocator);
defer beamsToAdd.deinit();
var beamsToRemove = std.ArrayList(usize).init(allocator);
defer beamsToRemove.deinit();
if (beams.items.len == 0) {
break;
}
for ((&beams).items, 0..) |*b, beamNumber| {
if (isOutOfGrid(b, grid)) {
try beamsToRemove.append(beamNumber);
continue;
}
try energized.put(b.coord, {});
if (beamHistory.contains(b.*)) {
try beamsToRemove.append(beamNumber);
continue;
}
try beamHistory.put(b.*, {});
const row = b.coord.row;
const col = b.coord.col;
const value = grid.items[row].items[col];
const goStraight = value == '.' or (value == '|' and (b.dir == .up or b.dir == .down)) or
(value == '-' and (b.dir == .left or b.dir == .right));
if (goStraight) {
switch (b.dir) {
.up => if (row == 0) {
b.coord.row = height + 10; // put it out of the grid to get cleaned up
} else {
b.coord.row -= 1;
},
.right => b.coord.col += 1,
.down => b.coord.row += 1,
.left => if (col == 0) {
b.coord.col = width + 10; // put it out of the grid to get cleaned up
} else {
b.coord.col -= 1;
},
}
} else if (value == '|') {
if (row == 0) {
// if we are on the top row, change the beam to go down
b.dir = Dir.down;
b.coord.row += 1;
} else {
// otherwise, change beam direction to up and move it up one cell
b.dir = Dir.up;
b.coord.row -= 1;
if (row != height - 1) {
// and if we're not on the _bottom_ row,
// create a new beam going down, below this cell
const newBeam = Beam{ .dir = Dir.down, .coord = Coord{ .row = row + 1, .col = col } };
try beamsToAdd.append(newBeam);
}
}
} else if (value == '-') {
if (col == 0) {
// if we are on the first col, change the beam to go right
b.dir = Dir.right;
b.coord.col += 1;
} else {
// otherwise, change beam direction to left and move it left one cell
b.dir = Dir.left;
b.coord.col -= 1;
if (col != width - 1) {
// and if we're not on the _last_ column,
// create a new beam going right, to the right this cell
const newBeam = Beam{ .dir = Dir.right, .coord = Coord{ .row = row, .col = col + 1 } };
try beamsToAdd.append(newBeam);
}
}
} else if (value == '/') {
switch (b.dir) {
.up => {
b.dir = Dir.right;
b.coord.col += 1;
},
.right => if (row == 0) {
b.coord.row = height + 10; // put it out of the grid to get cleaned up
} else {
b.dir = Dir.up;
b.coord.row -= 1;
},
.down => if (col == 0) {
b.coord.row = height + 10; // put it out of the grid to get cleaned up
} else {
b.dir = Dir.left;
b.coord.col -= 1;
},
.left => {
b.dir = Dir.down;
b.coord.row += 1;
},
}
} else if (value == '\\') {
switch (b.dir) {
.up => if (col == 0) {
b.coord.col = width + 10; // put it out of the grid to get cleaned up
} else {
b.dir = Dir.left;
b.coord.col -= 1;
},
.right => {
b.dir = Dir.down;
b.coord.row += 1;
},
.down => {
b.dir = Dir.right;
b.coord.col += 1;
},
.left => if (row == 0) {
b.coord.row = height + 10; // put it out of the grid to get cleaned up
} else {
b.dir = Dir.up;
b.coord.row -= 1;
},
}
}
}
// remove the beams in reverse order
const len = beamsToRemove.items.len;
for (0..len) |j| {
const idx = beamsToRemove.items[len - j - 1];
_ = beams.orderedRemove(idx);
}
beamsToRemove.clearAndFree();
// add the new beams
for (beamsToAdd.items) |beam| {
try beams.append(beam);
}
beamsToAdd.clearAndFree();
}
return energized.count();
}
fn isOutOfGrid(beam: *Beam, grid: std.ArrayList(std.ArrayList(u8))) bool {
const row = beam.coord.row;
const col = beam.coord.col;
const height = grid.items.len;
const width = grid.items[0].items.len;
return row < 0 or row >= height or col < 0 or col >= width;
}
fn printGrid(grid: std.ArrayList(std.ArrayList(u8)), energized: std.AutoHashMap(Coord, void)) void {
for (grid.items, 0..) |line, row| {
for (line.items, 0..) |char, col| {
if (char == '.' and energized.contains(Coord{ .row = row, .col = col })) {
std.debug.print("#", .{});
} else {
std.debug.print("{c}", .{char});
}
}
std.debug.print("\n", .{});
}
}
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