From f0b8e240a7e1dcc79c3f2109c6365dbbf7c67b46 Mon Sep 17 00:00:00 2001
From: cos <cos>
Date: Wed, 8 Dec 2021 21:51:54 +0100
Subject: Simplify set operations of 2021day08

Performing operations on sets using operators, rather than the less
ergonomic replaced methods, results readability improvements.
---
 2021/rust/day08/src/main.rs | 21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

diff --git a/2021/rust/day08/src/main.rs b/2021/rust/day08/src/main.rs
index f4e44bd..0eeb904 100644
--- a/2021/rust/day08/src/main.rs
+++ b/2021/rust/day08/src/main.rs
@@ -144,9 +144,7 @@ fn find_digits(input: &[Digit]) -> Result<Vec<Option<Digit>>> {
     }
     for unique_segments in [1, 4, 7, 8].into_iter() {
         // Digit 1 is found by unique number of segments, as in part 1.
-        // Digit 4 is found by unique number of segments, as in part 1.
-        // Digit 7 is found by unique number of segments, as in part 1.
-        // Digit 8 is found by unique number of segments, as in part 1.
+        // The same is true for Digit 4, Digit 7 and Digit 8.
         unknown.clone().into_iter().map(|d| if d.inner.len() == segment_count[unique_segments] {
             unknown.remove(&d);
             digits[unique_segments] = Some(d);
@@ -168,15 +166,12 @@ fn find_digits(input: &[Digit]) -> Result<Vec<Option<Digit>>> {
     digits[0] = unknown.clone().into_iter().filter(|d| {
         if let (Some(one), Some(three), Some(four), Some(eight)) =
             (&digits[1], &digits[3], &digits[4], &digits[8])
-            {
-                let set_a = four.inner.difference(&(one.inner)).cloned().collect();
-                let set_b = three.inner.intersection(&set_a).cloned().collect();
-                let set_c = eight.inner.difference(&set_b).cloned().collect();
-                if d.inner == set_c {
-                    unknown.remove(d);
-                    return true
-                }
+        {
+            if d.inner == &eight.inner - &(&three.inner & &(&four.inner - &one.inner)) {
+                unknown.remove(d);
+                return true
             }
+        }
         false
     }).last();
     digits[9] = unknown.clone().into_iter().filter(|d| {
@@ -200,9 +195,7 @@ fn find_digits(input: &[Digit]) -> Result<Vec<Option<Digit>>> {
     // Digit 2 is the one with zero overlap with the difference of Digit 4 - Digit 3.
     digits[2] = unknown.clone().into_iter().filter(|d| {
         if let (Some(three), Some(four)) = (&digits[3], &digits[4]) {
-            let set_a = four.inner.difference(&(three.inner)).cloned().collect();
-            let set_b: HashSet<Segment> = d.inner.intersection(&set_a).cloned().collect();
-            if set_b.is_empty() {
+            if (&d.inner & &(&four.inner - &three.inner)).is_empty() {
                 unknown.remove(d);
                 return true
             }
-- 
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