From 20de5928c29bd54822261f84c1b836c6c24818aa Mon Sep 17 00:00:00 2001
From: Matej Focko <mfocko@redhat.com>
Date: Tue, 12 Dec 2023 15:28:38 +0100
Subject: [PATCH] day(12): move the mutability into the function

Signed-off-by: Matej Focko <mfocko@redhat.com>
---
 src/bin/day12.rs | 45 ++++++++++++++++++++-------------------------
 1 file changed, 20 insertions(+), 25 deletions(-)

diff --git a/src/bin/day12.rs b/src/bin/day12.rs
index 1302f95..2e11548 100644
--- a/src/bin/day12.rs
+++ b/src/bin/day12.rs
@@ -30,11 +30,7 @@ impl FromStr for Row {
 }
 
 #[memoize]
-fn arrangements(
-    mut map: VecDeque<char>,
-    mut damaged: VecDeque<usize>,
-    mut in_damaged: bool,
-) -> usize {
+fn arrangements(map: VecDeque<char>, damaged: VecDeque<usize>, in_damaged: bool) -> usize {
     // all damaged have been placed
     if damaged.is_empty() {
         return if map.iter().all(|&c| c == '.' || c == '?') {
@@ -44,6 +40,10 @@ fn arrangements(
         };
     }
 
+    let mut map = map.clone();
+    let mut damaged = damaged.clone();
+    let mut in_damaged = in_damaged;
+
     // skip the functional
     while let Some('.') = map.front() {
         if in_damaged {
@@ -60,43 +60,38 @@ fn arrangements(
 
     match map[0] {
         '?' => {
-            map[0] = '#';
-            let as_non_functional = arrangements(map.clone(), damaged.clone(), true);
-
             map[0] = '.';
             let as_functional = if !in_damaged {
-                arrangements(map, damaged, false)
+                arrangements(map.clone(), damaged.clone(), false)
             } else {
                 0
             };
 
+            map[0] = '#';
+            let as_non_functional = arrangements(map, damaged, true);
+
             as_functional + as_non_functional
         }
         '#' if damaged.is_empty() => 0,
         '#' => {
             damaged[0] -= 1;
 
+            map.pop_front();
+
             if damaged[0] == 0 {
-                if 1 < map.len() && map[1] == '#' {
+                damaged.pop_front();
+
+                if let Some(&'#') = map.front() {
                     0
-                } else if 1 < map.len() {
-                    map[1] = '.';
-                    arrangements(
-                        map.iter().cloned().skip(1).collect(),
-                        damaged.iter().cloned().skip(1).collect(),
-                        false,
-                    )
+                } else if !map.is_empty() {
+                    map[0] = '.';
+                    arrangements(map, damaged, false)
                 } else {
-                    let result = arrangements(
-                        map.iter().cloned().skip(2).collect(),
-                        damaged.iter().cloned().skip(1).collect(),
-                        false,
-                    );
-                    result
+                    map.pop_front();
+                    arrangements(map, damaged, false)
                 }
             } else {
-                let result = arrangements(map.iter().cloned().skip(1).collect(), damaged, true);
-                result
+                arrangements(map, damaged, true)
             }
         }
         _ => unreachable!(),