195 lines
6.7 KiB
Zig
195 lines
6.7 KiB
Zig
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const std = @import("std");
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const example = @embedFile("example");
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const input = @embedFile("input");
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var allocator: std.mem.Allocator = undefined;
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pub fn main() anyerror!void {
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var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
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defer arena.deinit();
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allocator = arena.allocator();
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try std.testing.expectEqual(try solve(example), 24);
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const result = try solve(input);
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try std.io.getStdOut().writer().print("{}\n", .{result});
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}
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const Line = struct {
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data: std.ArrayList(u8),
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x: u64,
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fn get(l: *Line, x: u64) u8 {
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if (x >= l.x and x < l.x + @intCast(u64, l.len())) return l.data.items[@intCast(usize, x - @intCast(u64, l.x))];
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return ' ';
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}
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fn init() !*Line {
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var l = try allocator.create(Line);
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l.data = std.ArrayList(u8).init(allocator);
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return l;
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}
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inline fn len(l: Line) usize {
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return l.data.items.len;
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}
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fn set(l: *Line, x: u64, v: u8) !void {
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if (l.len() == 0) { // this is en empty line
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l.x = x;
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try l.data.append(v);
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return;
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}
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const lx = @intCast(u64, l.len());
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if (x >= l.x) {
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if (x < l.x + lx) { // just set the value
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l.data.items[@intCast(usize, x - l.x)] = v;
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} else { // we need to add trailing spaces
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var i: usize = l.len();
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while (i < x - l.x) : (i += 1) {
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try l.data.append(' ');
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}
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try l.data.append(v);
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}
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} else { // we need to shift right and add leading spaces
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const oldLen = l.len();
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l.data.items.len += @intCast(usize, l.x - x);
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try l.data.ensureUnusedCapacity(l.len());
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std.mem.copyBackwards(u8, l.data.items[@intCast(usize, l.x - x)..], l.data.items[0..oldLen]);
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l.data.items[0] = v;
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var i: usize = 1;
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while (i < @intCast(usize, l.x - x)) : (i += 1) {
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l.data.items[i] = ' ';
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}
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l.x = x;
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}
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}
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};
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pub const Field = struct {
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x: u64 = 0,
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y: u64 = 0,
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lines: std.ArrayList(*Line),
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lx: usize = 0,
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pub fn get(f: *Field, x: u64, y: u64) u8 {
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if (y >= f.y and y < f.y + @intCast(u64, f.lines.items.len)) return f.lines.items[@intCast(usize, y - @intCast(u64, f.y))].get(x);
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return ' ';
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}
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fn init() !*Field {
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var f = try allocator.create(Field);
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f.x = undefined;
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f.y = 0;
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f.lines = std.ArrayList(*Line).init(allocator);
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var l = try f.lines.addOne();
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l.* = try Line.init();
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f.lx = 0;
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return f;
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}
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inline fn isIn(f: *Field, x: u64, y: u64) bool {
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return x >= f.x and y >= f.y and x < f.x + @intCast(u64, f.lx) and y < f.y + @intCast(u64, f.lines.items.len);
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}
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inline fn len(f: Field) usize {
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return f.lines.items.len;
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}
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pub fn set(f: *Field, x: u64, y: u64, v: u8) !void {
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if (y >= f.y) {
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if (y < f.y + @intCast(u64, f.lines.items.len)) { // the line exists
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try f.lines.items[@intCast(usize, y - f.y)].set(x, v);
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} else { // append lines
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var i: usize = f.lines.items.len;
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while (i < y - f.y) : (i += 1) {
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try f.lines.append(try Line.init());
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}
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var l = try Line.init();
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try l.set(x, v);
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try f.lines.append(l);
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}
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} else { // preprend lines
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const oldLen = f.lines.items.len;
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f.lines.items.len += @intCast(usize, f.y - y);
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try f.lines.ensureUnusedCapacity(f.lines.items.len);
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std.mem.copyBackwards(*Line, f.lines.items[@intCast(usize, f.y - y)..], f.lines.items[0..oldLen]);
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var l = try Line.init();
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try l.set(x, v);
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f.lines.items[0] = l;
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var i: usize = 1;
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while (i < @intCast(usize, f.y - y)) : (i += 1) {
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f.lines.items[i] = try Line.init();
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}
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f.y = y;
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}
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if (x < f.x or x >= f.x + @intCast(u64, f.lx)) { // recalculate boundaries
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f.x = std.math.maxInt(u64);
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var x2: u64 = std.math.minInt(u64);
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for (f.lines.items) |line| {
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if (line.len() == 0) continue;
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if (f.x > line.x) f.x = line.x;
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if (x2 < line.x + @intCast(u64, line.len())) x2 = line.x + @intCast(u64, line.len());
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}
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f.lx = @intCast(usize, x2 - f.x);
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}
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return;
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}
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};
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fn solve(puzzle: []const u8) !u64 {
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var it = std.mem.tokenize(u8, puzzle, "\n");
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var field = try Field.init();
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// process input
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while (it.next()) |line| {
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var coords = std.mem.tokenize(u8, line, " ->,");
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var x = try std.fmt.parseInt(u64, coords.next() orelse continue, 10);
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var y = try std.fmt.parseInt(u64, coords.next() orelse unreachable, 10);
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try field.set(x, y, '#');
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while (true) {
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var a = try std.fmt.parseInt(u64, coords.next() orelse break, 10);
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var b = try std.fmt.parseInt(u64, coords.next() orelse unreachable, 10);
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while (x != a or y != b) {
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if (x < a) {
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x += 1;
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} else if (x > a) {
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x -= 1;
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}
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if (y < b) {
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y += 1;
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} else if (y > b) {
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y -= 1;
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}
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try field.set(x, y, '#');
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}
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}
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}
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// run simulation
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var i: usize = 0;
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outer: while (true) : (i += 1) { // add sand forever
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var x: u64 = 500;
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var y: u64 = field.y;
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while (true) { // let the sand fall
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if (!field.isIn(x, y)) {
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break :outer;
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}
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switch (field.get(x, y + 1)) {
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' ' => y += 1, // we can fall straight down
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else => {
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switch (field.get(x - 1, y + 1)) {
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' ' => { // we can fall down to the left
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x -= 1;
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y += 1;
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},
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else => {
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switch (field.get(x + 1, y + 1)) {
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' ' => { // we can fall down to the right
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x += 1;
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y += 1;
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},
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else => { // we stop falling
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try field.set(x, y, 'o');
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break;
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},
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}
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},
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}
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},
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}
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}
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}
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return i;
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}
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