diff --git a/src/day02.rs b/src/day02.rs
index c09c8ae..fabefae 100644
--- a/src/day02.rs
+++ b/src/day02.rs
@@ -1,4 +1,3 @@
-use std::cmp::max;
 use std::collections::HashSet;

 pub fn parse(contents: &str) -> Vec<(u64, u64)> {
@@ -14,6 +13,34 @@ fn num_digits(n: u64, b: u32) -> usize {
     (0..).take_while(|i| (b as u64).pow(*i) <= n).count()
 }

+// Returns the count of numbers with period `rep` between `id_start` and `id_end` (inclusive).
+fn count_between(rep: usize, id_start: u64, id_end: u64) -> i128 {
+    let digits_start = ((num_digits(id_start, 10) + (rep - 1)) / rep) as u32;
+    let digits_end = (num_digits(id_end, 10) / rep) as u32;
+    let mut count = 0;
+    for digits in digits_start..=digits_end {
+        let mut factor = 0;
+        for r in 0..rep as u32 {
+            factor += 10u64.pow(r * digits);
+        }
+
+        let mut invalid_check_start = 10u64.pow(digits - 1).max(id_start / factor);
+        if invalid_check_start * factor < id_start {
+            invalid_check_start += 1;
+        }
+
+        let end_invalid_ids = (10u64.pow(digits) - 1).min(id_end / factor);
+        if end_invalid_ids < invalid_check_start {
+            break;
+        }
+
+        let n = end_invalid_ids - invalid_check_start;
+        count += factor as i128
+            * ((n as i128 + 1) * invalid_check_start as i128 + ((n as i128 * (n as i128 + 1)) / 2));
+    }
+    count
+}
+
 // #[aoc(day2, part1)]
 #[allow(dead_code)]
 pub fn part_a(contents: &str) -> u64 {
@@ -70,29 +97,11 @@ pub fn part_a_binary(contents: &str) -> u64 {

 #[aoc(day2, part1, smarter)]
 // #[allow(dead_code)]
-pub fn part_a_smarter(contents: &str) -> u128 {
+pub fn part_a_smarter(contents: &str) -> i128 {
     let vec = parse(contents);
     let mut invalid_id_sum = 0;
     for (id_start, id_end) in vec {
-        let digits_start = (num_digits(id_start, 10) as f64 / 2.0).ceil() as usize;
-        let digits_end = max(num_digits(id_end, 10) / 2, 1);
-        for digits in digits_start..=digits_end {
-            let factor = 10u64.pow(digits as u32) + 1;
-
-            let mut invalid_check_start = 10u64.pow(digits as u32 - 1).max(id_start / factor);
-            while invalid_check_start * factor < id_start {
-                invalid_check_start += 1;
-            }
-
-            let end_invalid_ids = (10u64.pow(digits as u32) - 1).min(id_end / factor);
-            if end_invalid_ids < invalid_check_start {
-                continue;
-            }
-            let n = end_invalid_ids - invalid_check_start;
-            invalid_id_sum += factor as u128
-                * ((n + 1) as u128 * invalid_check_start as u128
-                    + ((n as u128 * (n as u128 + 1)) / 2));
-        }
+        invalid_id_sum += count_between(2, id_start, id_end);
     }
     invalid_id_sum
 }
@@ -198,36 +207,7 @@ pub fn part_b_smarter(contents: &str) -> i128 {
             continue;
         }
         for (id_start, id_end) in vec.iter() {
-            if num_digits(*id_end, 10) < rep {
-                continue;
-            }
-            let digits_start = (num_digits(*id_start, 10) as f64 / rep as f64).ceil() as usize;
-            let digits_end = num_digits(*id_end, 10) / rep;
-
-            for digits in digits_start..=digits_end {
-                let mut factor = 0;
-
-                for r in 0..rep {
-                    factor += 10u64.pow(r as u32 * digits as u32);
-                }
-
-                let mut invalid_check_start = 10u64.pow(digits as u32 - 1).max(*id_start / factor);
-
-                if invalid_check_start * factor < *id_start {
-                    invalid_check_start += 1;
-                }
-
-                let end_invalid_ids = (10u64.pow(digits as u32) - 1).min(id_end / factor);
-
-                if end_invalid_ids < invalid_check_start {
-                    continue;
-                }
-                let n = end_invalid_ids - invalid_check_start;
-                invalid_id_sum += sign as i128
-                    * factor as i128
-                    * ((n + 1) as i128 * invalid_check_start as i128
-                        + ((n as i128 * (n as i128 + 1)) / 2));
-            }
+            invalid_id_sum += sign as i128 * count_between(rep, *id_start, *id_end);
         }
     }
     invalid_id_sum