refactor 51

src/euler51/Cargo.toml

@@ -8,3 +8,6 @@ edition = "2021"
 [dependencies]
 primes = {version = "*", path = "../../lib/primes"}
 combination = {version = "*", path = "../../lib/combination"}
+
+[profile.release]
+debug = true

src/euler51/src/main.rs

@@ -43,12 +43,7 @@ fn main() {
             let mut primes_matching_pattern = vec![];
             let digits = first.to_digits();
             for digit in DIGITS {
-                let could_be_prime = digits
-                    .iter()
-                    .zip(pattern.clone())
-                    .map(|(d, b)| if b { digit } else { *d })
-                    .collect::<Vec<u8>>()
-                    .to_num();
+                let could_be_prime = apply_transformation(&digits, digit, &pattern);
                 if primes_to_check.contains(&could_be_prime) || could_be_prime == first {
                     primes_matching_pattern.push(could_be_prime);
                 }
@@ -64,6 +59,24 @@ fn main() {
     println!("{:#?}", get_longest(best_of_all_combinations, false));
 }
 
+fn apply_transformation(prime_as_digits: &[u8], new_digit: u8, pattern: &[bool]) -> Int {
+    debug_assert_eq!(prime_as_digits.len(), pattern.len());
+    let mut multiplier = 1;
+    let result = prime_as_digits
+        .iter()
+        .zip(pattern)
+        .map(|(old_digit, replace)| if *replace { new_digit } else { *old_digit })
+        .map(|d| d as Int)
+        .rev()
+        .reduce(|accum, item| {
+            multiplier *= 10;
+            accum + multiplier * item
+        })
+        .unwrap();
+    debug_assert_eq!(multiplier, 100_000);
+    result
+}
+
 fn get_longest(mut vec: Vec<Vec<Int>>, print: bool) -> Vec<Int> {
     if vec.is_empty() {
         panic!("cannot give the longest element of an empty vector")
@@ -107,7 +120,7 @@ impl ToNum for Vec<u8> {
 
 #[cfg(test)]
 mod test {
-    use crate::{ToDigits, ToNum};
+    use crate::{apply_transformation, ToDigits, ToNum};
 
     #[test]
     fn test_digits_to_num() {
@@ -120,4 +133,15 @@ mod test {
         let num = 83371;
         assert_eq!(num.to_digits(), vec![8, 3, 3, 7, 1]);
     }
+
+    #[test]
+    fn test_apply_transformation() {
+        let prime_as_digits = [5, 7, 3, 8, 2, 1];
+        let new_digit = 0;
+        let pattern = [false, true, true, true, false, false];
+        assert_eq!(
+            apply_transformation(&prime_as_digits, new_digit, &pattern),
+            500_021
+        );
+    }
 }