Solve Day 1 Part 2

Author: destinationunknown

src/bin/01.rs

@@ -1,5 +1,7 @@
 advent_of_code::solution!(1);
 
+use std::collections::HashMap;
+
 pub fn part_one(input: &str) -> Option<u32> {
     // read input into two lists
     let (mut a, mut b): (Vec<u32>, Vec<u32>) = input
@@ -25,7 +27,28 @@ pub fn part_one(input: &str) -> Option<u32> {
 }
 
 pub fn part_two(input: &str) -> Option<u32> {
-    None
+    // read input into two lists
+    let (a, b): (Vec<u32>, Vec<u32>) = input
+        .lines()
+        .filter_map(|line| {
+            let mut parts = line.split_whitespace();
+            let first = parts.next()?.parse::<u32>().ok()?;
+            let second = parts.next()?.parse::<u32>().ok()?;
+            Some((first, second))
+        })
+        .unzip();
+
+    let b_freq = b.into_iter().fold(HashMap::new(), |mut map, val| {
+        *map.entry(val).or_insert(0) += 1;
+        map
+    });
+
+    let similarity_score: u32 = a
+        .iter()
+        .map(|x| x * b_freq.get(x).unwrap_or(&0))
+        .sum();
+
+    Some(similarity_score)
 }
 
 #[cfg(test)]
@@ -41,6 +64,6 @@ mod tests {
     #[test]
     fn test_part_two() {
         let result = part_two(&advent_of_code::template::read_file("examples", DAY));
-        assert_eq!(result, None);
+        assert_eq!(result, Some(31));
     }
 }