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const std = @import("std");
const mecha = @import("mecha");
const print = std.debug.print;
pub fn solve(part: []u8, buffer: []u8, allocator: std.mem.Allocator) !void {
var lines = std.mem.splitScalar(u8, buffer, '\n');
var grid = std.ArrayList([]u8).init(allocator);
defer grid.deinit();
var x: i32 = 0;
var y: i32 = 0;
var row: usize = 0;
while (lines.next()) |line| : (row += 1) {
for (line, 0..) |element, i| {
if (element == '^') {
x = @intCast(i);
y = @intCast(row);
}
}
try grid.append(@constCast(line));
}
if (std.mem.eql(u8, part, "1")) {
try part1(&grid, x, y, allocator);
} else {
try part2(&grid, x, y, allocator);
}
}
fn locations(grid: *std.ArrayList([]u8), startx: i32, starty: i32, allocator: std.mem.Allocator) !std.AutoHashMap(std.meta.Tuple(&.{ i32, i32, i32, i32 }), void) {
var dirx: i32 = 0;
var diry: i32 = -1;
var x = startx;
var y = starty;
var history = try allocator.alloc(bool, grid.items.len * grid.items[0].len * 4);
defer allocator.free(history);
for (history) |*elem| {
elem.* = false;
}
var unique = std.AutoHashMap(std.meta.Tuple(&.{ i32, i32, i32, i32 }), void).init(allocator);
errdefer unique.deinit();
const width: i32 = @intCast(grid.items[0].len);
while (y >= 0 and y < grid.items.len and x >= 0 and x < grid.items[@intCast(y)].len) {
if (!history[@intCast(y * width + x)] and grid.items[@intCast(y)][@intCast(x)] != '#') {
try unique.put(.{ x, y, dirx, diry }, {});
history[@intCast(y * width + x)] = true;
}
if (grid.items[@intCast(y)][@intCast(x)] == '#') {
x -= dirx;
y -= diry;
const temp = dirx;
dirx = -diry;
diry = temp;
}
x += dirx;
y += diry;
}
return unique;
}
fn part1(grid: *std.ArrayList([]u8), startx: i32, starty: i32, allocator: std.mem.Allocator) !void {
var locs = try locations(grid, startx, starty, allocator);
defer locs.deinit();
print("{d}\n", .{locs.count()});
}
//----------------------------PART 2---------------------------------------------
fn directionToIndex(dirx: i32, diry: i32) i32 {
if (dirx == 0 and diry == -1) {
return 0;
} else if (dirx == 1 and diry == 0) {
return 1;
} else if (dirx == 0 and diry == 1) {
return 2;
} else {
return 3;
}
}
fn part2(grid: *std.ArrayList([]u8), startx: i32, starty: i32, allocator: std.mem.Allocator) !void {
var locs = try locations(grid, startx, starty, allocator);
defer locs.deinit();
var total: usize = 0;
var iterator = locs.keyIterator();
var history = try allocator.alloc(bool, grid.items.len * grid.items[0].len * 4);
defer allocator.free(history);
const width: i32 = @intCast(grid.items[0].len);
while (iterator.next()) |location| {
grid.items[@intCast(location[1])][@intCast(location[0])] = '#';
var dirx: i32 = location[2];
var diry: i32 = location[3];
var x = location[0];
var y = location[1];
for (history) |*elem| {
elem.* = false;
}
while (y >= 0 and y < grid.items.len and x >= 0 and x < grid.items[@intCast(y)].len) {
const index = y * width * 4 + x * 4 + directionToIndex(dirx, diry);
if (history[@intCast(index)]) {
total += 1;
break;
}
if (grid.items[@intCast(y)][@intCast(x)] == '#') {
x -= dirx;
y -= diry;
const temp = dirx;
dirx = -diry;
diry = temp;
}
history[@intCast(index)] = true;
x += dirx;
y += diry;
}
grid.items[@intCast(location[1])][@intCast(location[0])] = '.';
}
print("{d}\n", .{total});
}
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