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const std = @import("std");
const example = @embedFile("example");
const example2 = @embedFile("example2");
const input = @embedFile("input");
pub fn main() anyerror!void {
var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
defer arena.deinit();
const allocator = arena.allocator();
try std.testing.expectEqual(try solve(example, allocator), 1);
try std.testing.expectEqual(try solve(example2, allocator), 36);
const result = try solve(input, allocator);
try std.io.getStdOut().writer().print("{}\n", .{result});
}
const Line = struct {
data: std.ArrayList(bool),
x: i64,
fn init(allocator: std.mem.Allocator) !*Line {
var l = try allocator.create(Line);
l.data = std.ArrayList(bool).init(allocator);
return l;
}
inline fn len(l: Line) usize {
return l.data.items.len;
}
fn set(l: *Line, x: i64) !void {
if (l.len() == 0) { // this is en empty line
l.x = x;
try l.data.append(true);
return;
}
const lx = @intCast(i64, l.len());
if (x >= l.x) {
if (x < l.x + lx) { // just set the value
l.data.items[@intCast(usize, x - l.x)] = true;
} else { // we need to add trailing spaces
var i: usize = l.len();
while (i < x - l.x) : (i += 1) {
try l.data.append(false);
}
try l.data.append(true);
}
} 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(bool, l.data.items[@intCast(usize, l.x - x)..], l.data.items[0..oldLen]);
l.data.items[0] = true;
var i: usize = 1;
while (i < @intCast(usize, l.x - x)) : (i += 1) {
l.data.items[i] = false;
}
l.x = x;
}
}
pub fn visited(l: Line) u64 {
var tot: u64 = 0;
var i: usize = 0;
while (i < l.len()) : (i += 1) {
if (l.data.items[i]) {
tot += 1;
}
}
return tot;
}
};
pub const Field = struct {
allocator: std.mem.Allocator,
x: i64 = 0,
y: i64 = 0,
lines: std.ArrayList(*Line),
lx: usize = 0,
fn init(allocator: std.mem.Allocator) !*Field {
var f = try allocator.create(Field);
f.allocator = allocator;
f.x = undefined;
f.y = 0;
f.lines = std.ArrayList(*Line).init(allocator);
var l = try f.lines.addOne();
l.* = try Line.init(allocator);
f.lx = 0;
return f;
}
inline fn len(f: Field) usize {
return f.lines.items.len;
}
pub fn set(f: *Field, x: i64, y: i64) !void {
if (y >= f.y) {
if (y < f.y + @intCast(i64, f.lines.items.len)) { // the line exists
try f.lines.items[@intCast(usize, y - f.y)].set(x);
} else { // append lines
var i: usize = f.lines.items.len;
while (i < y - f.y) : (i += 1) {
try f.lines.append(try Line.init(f.allocator));
}
var l = try Line.init(f.allocator);
try l.set(x);
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(f.allocator);
try l.set(x);
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.allocator);
}
f.y = y;
}
if (x < f.x or x >= f.x + @intCast(i64, f.lx)) { // recalculate boundaries
f.x = std.math.maxInt(i64);
var x2: i64 = std.math.minInt(i64);
for (f.lines.items) |line| {
if (line.len() == 0) continue;
if (f.x > line.x) f.x = line.x;
if (x2 < line.x + @intCast(i64, line.len())) x2 = line.x + @intCast(i64, line.len());
}
f.lx = @intCast(usize, x2 - f.x);
}
return;
}
pub fn visited(f: Field) u64 {
var tot: u64 = 0;
var i: usize = 0;
while (i < f.len()) : (i += 1) {
tot += f.lines.items[i].visited();
}
return tot;
}
};
const Rope = struct {
hx: i64 = 0,
hy: i64 = 0,
tx: i64 = 0,
ty: i64 = 0,
fn stepH(r: *Rope, direction: u8) void {
switch (direction) {
'D' => {
r.hy += 1;
},
'L' => {
r.hx -= 1;
},
'R' => {
r.hx += 1;
},
'U' => {
r.hy -= 1;
},
else => unreachable,
}
}
fn stepT(r: *Rope) void {
if (r.tx == r.hx) { // same line
if (r.ty + 2 == r.hy) { // to the left
r.ty += 1;
} else if (r.ty - 2 == r.hy) { // to the right
r.ty -= 1;
}
} else if (r.ty == r.hy) { // same column
if (r.tx + 2 == r.hx) { // to the top
r.tx += 1;
} else if (r.tx - 2 == r.hx) { // to the bottom
r.tx -= 1;
}
} else if (r.tx + 1 == r.hx) { // on the left by one
if (r.ty + 2 == r.hy) { // above by two
r.tx += 1;
r.ty += 1;
} else if (r.ty - 2 == r.hy) { // bellow by two
r.tx += 1;
r.ty -= 1;
}
} else if (r.tx - 1 == r.hx) { // on the right by one
if (r.ty + 2 == r.hy) { // above by two
r.tx -= 1;
r.ty += 1;
} else if (r.ty - 2 == r.hy) { // bellow by two
r.tx -= 1;
r.ty -= 1;
}
} else if (r.ty + 1 == r.hy) { // above by one
if (r.tx + 2 == r.hx) { // two to the left
r.tx += 1;
r.ty += 1;
} else if (r.tx - 2 == r.hx) { // two to the right
r.tx -= 1;
r.ty += 1;
}
} else if (r.ty - 1 == r.hy) { // bellow by one
if (r.tx + 2 == r.hx) { // two to the left
r.tx += 1;
r.ty -= 1;
} else if (r.tx - 2 == r.hx) { // two to the right
r.tx -= 1;
r.ty -= 1;
}
} else {
if (r.tx + 2 == r.hx) { // far left
r.tx += 1;
} else if (r.tx - 2 == r.hx) { // far right
r.tx -= 1;
}
if (r.ty + 2 == r.hy) { // far above
r.ty += 1;
} else if (r.ty - 2 == r.hy) { // far bellow
r.ty -= 1;
}
}
}
};
fn solve(puzzle: []const u8, allocator: std.mem.Allocator) !u64 {
var it = std.mem.tokenize(u8, puzzle, "\n");
var rope: [9]Rope = undefined;
for (rope) |*r| {
r.* = Rope{};
}
var field = try Field.init(allocator);
// process input
while (it.next()) |line| {
var elts = std.mem.split(u8, line, " ");
_ = elts.next() orelse unreachable; // the move word
var n = try std.fmt.parseInt(u8, elts.next() orelse unreachable, 10);
while (n > 0) : (n -= 1) {
rope[0].stepH(line[0]);
rope[0].stepT();
var i: usize = 1;
while (i < rope.len) : (i += 1) {
rope[i].hx = rope[i - 1].tx;
rope[i].hy = rope[i - 1].ty;
rope[i].stepT();
}
try field.set(rope[rope.len - 1].tx, rope[rope.len - 1].ty);
}
}
return field.visited();
}
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