diff --git a/src/lib.rs b/src/lib.rs
index 55a2f04..0535e93 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,4 +1,4 @@
-pub fn day1_part1(input: &str) -> String {
+pub fn day1_preprocess(input: &str) -> (Vec<u32>, Vec<u32>) {
     let pairs: Vec<Vec<u32>> = input
         .lines()
         .map(|line| {
@@ -12,11 +12,32 @@ pub fn day1_part1(input: &str) -> String {
     let mut right = pairs.iter().map(|pair| pair[1]).collect::<Vec<_>>();
     left.sort();
     right.sort();
-
-    let sum: u32 = left.iter().zip(right).map(|(left, right)| left.abs_diff(right)).sum();
+    (left, right)
+}
+pub fn day1_part1(input: &str) -> String {
+    let (left, right) = day1_preprocess(input);
+    let sum: u32 = left
+        .iter()
+        .zip(right)
+        .map(|(left, right)| left.abs_diff(right))
+        .sum();
     sum.to_string()
 }
 
+pub fn day1_part2(input: &str) -> String {
+    let (left, right) = day1_preprocess(input);
+    let similarity_score: u32 = left.into_iter()
+        .map(|left_location| {
+            left_location
+                * right
+                    .iter()
+                    .filter(|&&right_location| right_location == left_location)
+                    .count() as u32
+        })
+        .sum();
+    similarity_score.to_string()
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -28,4 +49,12 @@ mod tests {
         let result = day1_part1(include_str!("../input/day1.txt"));
         assert_eq!(result, "2742123");
     }
+
+    #[test]
+    fn day1_part2_test() {
+        let test_result = day1_part2(include_str!("../input/day1_part1.test.txt"));
+        assert_eq!(test_result, "31");
+        let result = day1_part2(include_str!("../input/day1.txt"));
+        assert_eq!(result, "21328497");
+    }
 }