chore: optimize by not using regex

Author: clechasseur

Cargo.lock

@@ -8,7 +8,6 @@ rust-version = "1.81.0"
 aoclp = { path = "../aoclp" }
 bit-vec = { workspace = true }
 clap = { workspace = true, features = ["derive"] }
-fancy-regex = { workspace = true }
 itertools = { workspace = true }
 paste = { workspace = true }
 primes = { workspace = true }

aoclp_solutions/Cargo.toml

@@ -3,24 +3,21 @@ use std::str::FromStr;
 
 use aoclp::num::Integer;
 use aoclp::solvers_impl::input::safe_get_input_as_one_vec;
-use fancy_regex::Regex;
 use itertools::Itertools;
 
 pub fn part_1() -> usize {
-    let re = Regex::new(r"^(\d+)\1$").unwrap();
-    sum_of_invalid(&re)
+    input()
+        .into_iter()
+        .flat_map(|range| range.into_iter())
+        .filter(|id| invalid(*id))
+        .sum()
 }
 
 pub fn part_2() -> usize {
-    let re = Regex::new(r"^(\d+)(\1)+$").unwrap();
-    sum_of_invalid(&re)
-}
-
-fn sum_of_invalid(re: &Regex) -> usize {
     input()
         .into_iter()
         .flat_map(|range| range.into_iter())
-        .filter(|id| re.is_match(&id.to_string()).unwrap())
+        .filter(|id| invalid_fancy(*id))
         .sum()
 }
 
@@ -38,6 +35,29 @@ fn invalid(id: usize) -> bool {
     false
 }
 
+fn invalid_fancy(id: usize) -> bool {
+    let num_digits = num_digits(id);
+    (1..=num_digits / 2).any(|of_size| invalid_of_size(id, num_digits, of_size))
+}
+
+fn invalid_of_size(mut id: usize, num_digits: usize, of_size: usize) -> bool {
+    if num_digits % of_size == 0 {
+        let window = 10usize.pow(of_size as u32);
+        let expected = id % window;
+        while id != 0 {
+            let actual = id % window;
+            id /= window;
+            if actual != expected {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    false
+}
+
 struct IdRange(RangeInclusive<usize>);
 
 impl IntoIterator for IdRange {