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const std = @import("std");
const Galaxy = struct { row: usize, col: usize };
pub fn main() !void {
const content = @embedFile("data.txt");
var gpa = std.heap.GeneralPurposeAllocator(.{}){};
const allocator = gpa.allocator();
// put into ArrayList of ArrayLists
var grid = try parseGrid(content, allocator);
defer grid.deinit();
std.debug.print("grid: {any}\n", .{grid});
// find empty rows
const emptyRows = try findEmptyRows(grid, allocator);
std.debug.print("empty rows: {any}\n", .{emptyRows});
// find empty columns
const emptyColumns = try findEmptyColumns(grid, allocator);
std.debug.print("empty cols: {any}\n", .{emptyColumns});
// duplicate empty rows
// NOTE: not doing this any more, using Part 2 solution for Part 1
//
// for (emptyRows.items, 0..) |row, i| {
// try grid.insert(row + i, grid.items[row + i]);
// }
//
// // duplicate empty columns
// for (emptyColumns.items, 0..) |col, i| {
// for (grid.items, 0..) |_, row| {
// try grid.items[row].insert(col + i, '.');
// }
// }
// find original galaxy locations
var galaxies = std.ArrayList(Galaxy).init(allocator);
for (grid.items, 0..) |row, i| {
for (row.items, 0..) |char, j| {
if (char == '#') {
try galaxies.append(Galaxy{ .row = i, .col = j });
}
}
}
var galaxies1 = std.ArrayList(Galaxy).init(allocator);
var galaxies2 = std.ArrayList(Galaxy).init(allocator);
for (galaxies.items) |g| {
const row = g.row;
const col = g.col;
// how many expanded rows & cols before this galaxy?
var expandedRows: usize = 0;
for (emptyRows.items) |r| {
if (r > row) {
break;
}
expandedRows += 1;
}
var expandedColumns: usize = 0;
for (emptyColumns.items) |c| {
if (c > col) {
break;
}
expandedColumns += 1;
}
const expansionFactor = 1_000_000;
try galaxies1.append(Galaxy{ .row = row + expandedRows, .col = col + expandedColumns });
try galaxies2.append(Galaxy{ .row = row + (expansionFactor - 1) * expandedRows, .col = col + (expansionFactor - 1) * expandedColumns });
}
// add up all their distances
var part1: usize = 0;
for (0..galaxies1.items.len - 1) |i| {
for (i + 1..galaxies1.items.len) |j| {
part1 += dist(galaxies1.items[j], galaxies1.items[i]);
}
}
std.debug.print("Part 1: {d}\n", .{part1});
var part2: usize = 0;
for (0..galaxies2.items.len - 1) |i| {
for (i + 1..galaxies2.items.len) |j| {
part2 += dist(galaxies2.items[j], galaxies2.items[i]);
}
}
std.debug.print("Part 2: {d}\n", .{part2});
}
fn dist(a: Galaxy, b: Galaxy) usize {
const x = if (a.row > b.row) a.row - b.row else b.row - a.row;
const y = if (a.col > b.col) a.col - b.col else b.col - a.col;
return x + y;
}
fn findEmptyColumns(grid: std.ArrayList(std.ArrayList(u8)), allocator: std.mem.Allocator) !std.ArrayList(usize) {
var cols = std.ArrayList(usize).init(allocator);
const height = grid.items.len;
const width = grid.items[0].items.len;
for (0..width) |col| {
var allEmpty = true;
for (0..height) |row| {
if (grid.items[row].items[col] == '#') {
allEmpty = false;
}
}
if (allEmpty) {
try cols.append(col);
}
}
return cols;
}
fn findEmptyRows(grid: std.ArrayList(std.ArrayList(u8)), allocator: std.mem.Allocator) !std.ArrayList(usize) {
var rows = std.ArrayList(usize).init(allocator);
for (grid.items, 0..) |row, idx| {
var allEmpty = true;
for (row.items) |char| {
if (char == '#') {
allEmpty = false;
}
}
if (allEmpty) {
try rows.append(idx);
}
}
return rows;
}
fn parseGrid(content: []const u8, allocator: std.mem.Allocator) !std.ArrayList(std.ArrayList(u8)) {
var grid = std.ArrayList(std.ArrayList(u8)).init(allocator);
var lines = std.mem.split(u8, content, "\n");
while (lines.next()) |line| {
if (line.len < 1) {
break;
}
var al = std.ArrayList(u8).init(allocator);
for (line) |char| {
try al.append(char);
}
try grid.append(al);
}
return grid;
}