From 7748a536ebcd4a3a08360c80529df9d89ea04a29 Mon Sep 17 00:00:00 2001
From: Reiner Herrmann <reiner@reiner-h.de>
Date: Sun, 1 Dec 2024 13:30:27 +0100
Subject: day1 solution 2

---
 src/bin/day1.rs | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/src/bin/day1.rs b/src/bin/day1.rs
index d0c9bae..f1c6c80 100644
--- a/src/bin/day1.rs
+++ b/src/bin/day1.rs
@@ -3,17 +3,22 @@ static DAY: u8 = 1;
 fn main() {
     let input = advent::read_lines(DAY);
     println!("{DAY}a: {}", list_distance(&input));
-    println!("{DAY}b: {}", 0);
+    println!("{DAY}b: {}", similarity(&input));
 }
 
-fn list_distance(numbers: &[String]) -> u32 {
+fn parse_numbers(numbers: &[String]) -> (Vec::<usize>, Vec::<usize>) {
     let mut list1 = Vec::new();
     let mut list2 = Vec::new();
     for pair in numbers {
         let (number1, number2) = pair.split_once("   ").unwrap();
-        list1.push(number1.parse::<u32>().unwrap());
-        list2.push(number2.parse::<u32>().unwrap());
+        list1.push(number1.parse::<usize>().unwrap());
+        list2.push(number2.parse::<usize>().unwrap());
     }
+    (list1, list2)
+}
+
+fn list_distance(numbers: &[String]) -> usize {
+    let (mut list1, mut list2) = parse_numbers(numbers);
     list1.sort();
     list2.sort();
 
@@ -23,6 +28,14 @@ fn list_distance(numbers: &[String]) -> u32 {
          .sum()
 }
 
+fn similarity(numbers: &[String]) -> usize {
+    let (list1, list2) = parse_numbers(numbers);
+
+    list1.iter()
+         .map(|x| x * list2.iter().filter(|&y| x == y).count())
+         .sum()
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -38,5 +51,6 @@ mod tests {
             "3   3",
         ].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
         assert_eq!(list_distance(&input), 11);
+        assert_eq!(similarity(&input), 31);
     }
 }
-- 
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