refactor day 7 to be more iterator-y

src/day07.rs

@@ -11,7 +11,7 @@ pub fn process_part_1(input: &str) -> u32 {
     let (_, commands) = parse_commands(input).unwrap();
     let directories = build_directory_tree_from_commands(commands);
 
-    directories.values().filter(|size| **size <= 100_000).sum()
+    directories.values().filter(|&size| *size <= 100_000).sum()
 }
 
 pub fn process_part_2(input: &str) -> u32 {
@@ -25,44 +25,48 @@ pub fn process_part_2(input: &str) -> u32 {
 
     directories
         .values()
-        .filter(|size| **size >= wanted_space)
-        .map(|size| *size)
+        .filter(|&size| *size >= wanted_space)
+        .map(|&size| size)
         .min()
         .unwrap_or(0)
 }
 
 fn build_directory_tree_from_commands(commands: Vec<Command>) -> BTreeMap<String, u32> {
-    let mut cwd: Vec<&str> = vec![];
-    let mut directories: BTreeMap<String, u32> = BTreeMap::new();
-    for command in commands {
-        match command {
-            Command::Cd("/") => {
-                cwd = vec![];
-            }
-            Command::Cd("..") => {
-                cwd.pop();
-            }
-            Command::Cd(name) => {
-                cwd.push(name);
-            }
-            Command::Ls(files) => {
-                for file in files {
-                    match file {
-                        DirEntry::File { name: _name, size } => {
-                            for i in 0..=cwd.len() {
-                                directories
-                                    .entry(cwd[..i].join("/"))
-                                    .and_modify(|f| *f += size)
-                                    .or_insert(size);
-                            }
-                        }
-                        _ => {}
+    commands
+        .iter()
+        .fold((vec![], BTreeMap::new()), |(mut cwd, mut dirs), command| {
+            match command {
+                Command::Cd("/") => {
+                    cwd = vec![];
+                }
+                Command::Cd("..") => {
+                    cwd.pop();
+                }
+                Command::Cd(dir) => {
+                    cwd.push(*dir);
+                }
+                Command::Ls(files) => {
+                    // We don't actually care about individual files, just sum the files together
+                    // so we aren't looking up the BTreeMap as often
+                    let total_size = files
+                        .iter()
+                        .filter_map(|e| match e {
+                            DirEntry::File { size, .. } => Some(size),
+                            _ => None,
+                        })
+                        .sum();
+
+                    for i in 0..=cwd.len() {
+                        dirs.entry(cwd[..i].join("/"))
+                            .and_modify(|f| *f += total_size)
+                            .or_insert(total_size);
                     }
                 }
             }
-        }
-    }
-    directories
+
+            (cwd, dirs)
+        })
+        .1
 }
 
 #[derive(Debug)]
@@ -74,7 +78,11 @@ enum Command<'a> {
 #[derive(Debug)]
 enum DirEntry<'a> {
     Dir(&'a str),
-    File { name: &'a str, size: u32 },
+    #[allow(dead_code)]
+    File {
+        name: &'a str,
+        size: u32,
+    },
 }
 
 fn parse_commands(input: &str) -> IResult<&str, Vec<Command>> {