67 lines
2.2 KiB
Zig
67 lines
2.2 KiB
Zig
const std = @import("std");
|
|
|
|
const example = @embedFile("example");
|
|
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), 24933642);
|
|
const result = try solve(input, allocator);
|
|
try std.io.getStdOut().writer().print("{}\n", .{result});
|
|
}
|
|
|
|
fn solve(puzzle: []const u8, allocator: std.mem.Allocator) !u64 {
|
|
var it = std.mem.tokenize(u8, puzzle, "\n");
|
|
var tot: usize = 0;
|
|
var n: usize = 0; // depth
|
|
var sizes = std.ArrayList(u64).init(allocator);
|
|
var stack = std.ArrayList(u64).init(allocator);
|
|
_ = it.next() orelse unreachable; // drop the cd /
|
|
try stack.append(0);
|
|
while (it.next()) |line| {
|
|
if (line[2] == 'c') { // a cd command
|
|
if (line[5] == '.') { // going up
|
|
const v = stack.pop();
|
|
n -= 1;
|
|
stack.items[n] += v;
|
|
try sizes.append(v);
|
|
} else { // going down
|
|
n += 1;
|
|
try stack.append(0);
|
|
}
|
|
} else if (line[2] == 'l') { // a ls command
|
|
continue;
|
|
} else if (line[2] == 'r') { // a dir entry in a ls command
|
|
continue;
|
|
} else { // a file entry in a ls command
|
|
var elts = std.mem.split(u8, line, " ");
|
|
const v = try std.fmt.parseInt(u64, elts.next() orelse unreachable, 10);
|
|
stack.items[n] += v;
|
|
tot += v;
|
|
}
|
|
}
|
|
while (n > 1) : (n -= 1) { // we unwrap the cd up to /
|
|
const v = stack.pop();
|
|
n -= 1;
|
|
stack.items[n] += v;
|
|
try sizes.append(v);
|
|
}
|
|
try sizes.append(stack.items[n]); // we do not forget the last one
|
|
n = 30000000 - (70000000 - tot); // the amount of space we need to free
|
|
// let's run a dychotomy on the array
|
|
std.sort.sort(u64, sizes.items, {}, std.sort.asc(u64));
|
|
var a: usize = 0;
|
|
var b = sizes.items.len - 1;
|
|
while (b - a > 2) {
|
|
const m = a + (b - a) / 2;
|
|
if (sizes.items[m] < n) {
|
|
a = m;
|
|
} else {
|
|
b = m;
|
|
}
|
|
}
|
|
return sizes.items[b];
|
|
}
|