add day 7, part 2

day07/part2.rs

@@ -0,0 +1,49 @@
+// Copyright 2022 Christian Ulrich
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+// usage: ./part2 < input
+
+pub mod common;
+
+use common::{FileSystem, Node};
+
+const DISK_SIZE: usize = 70000000;
+const SPACE_REQUIRED: usize = 30000000;
+
+fn main() -> Result<(), &'static str> {
+    let fs = FileSystem::from_stdin()?;
+    let total_size = fs.root().size();
+    let free_space = DISK_SIZE - total_size;
+    if free_space >= SPACE_REQUIRED {
+        return Err("Sufficient free space, nothing to be done!");
+    }
+    // we need to find a directory of at least this size
+    let min_directory_size = SPACE_REQUIRED - free_space;
+    let mut result = total_size;
+    for node in fs.root().walk() {
+        if let Node::Directory {
+            name: _,
+            children: _,
+        } = node
+        {
+            let size = node.size();
+            if size >= min_directory_size && size < result {
+                result = size;
+            }
+        }
+    }
+    println!("{result}");
+    Ok(())
+}