day07: Changes for part 2

Now that we have the sizes of the directories in a list, it's quite easy
to work with them to get part 2 using Iterator functions.

day07/src/main.rs

@@ -153,8 +153,9 @@ fn main() -> Result<(), Box<dyn error::Error>> {
 
 	// compute sizes
 	let sizes = fs_tree.get_dir_sizes();
-	println!("{}", sizes.iter().filter(|x| **x < 100000).sum::<u32>());
+	let full_space = 70000000;
-
+	let free_space = full_space - sizes[sizes.len() - 1];
-    println!("Hello, world!");
+	let needed_space = 30000000 - free_space;
+	println!("{}", sizes.iter().filter(|x| **x > needed_space).min().unwrap());
     Ok(())
 }