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