From 799516005fe6adb49260eb51c8d31891b4ac8749 Mon Sep 17 00:00:00 2001
From: "Dr. Matthias Ratajczak" <m.ratajczak@hzdr.de>
Date: Tue, 16 Aug 2022 18:59:17 +0200
Subject: [PATCH] more performance optimizations for 51

---
 lib/primes/src/lib.rs   | 12 +++++--
 src/euler51/src/main.rs | 75 ++++++++++++++++++++++++++++++++---------
 2 files changed, 68 insertions(+), 19 deletions(-)

diff --git a/lib/primes/src/lib.rs b/lib/primes/src/lib.rs
index 8cfaaef..f99018d 100644
--- a/lib/primes/src/lib.rs
+++ b/lib/primes/src/lib.rs
@@ -12,7 +12,7 @@ use num::ToPrimitive;
 
 #[derive(Clone)]
 pub struct Primes<T> {
-    vector: Vec<T>,
+    pub vector: Vec<T>,
     set: HashSet<T>,
 }
 
@@ -157,14 +157,20 @@ mod test {
 
     #[ignore]
     #[test]
-    fn test_performance() {
+    fn test_performance_1() {
+        let _ = Primes::get_between(100_000, 999_999);
+    }
+
+    #[ignore]
+    #[test]
+    fn test_performance_2() {
         let primes = Primes::get_between(2, 10_000_000);
         assert_eq!(primes.len(), 664_579);
     }
 
     #[ignore]
     #[test]
-    fn test_performance_2() {
+    fn test_performance_3() {
         let primes = Primes::get_between(2, 1_000_000_000);
         assert_eq!(primes.len(), 50_847_534);
     }
diff --git a/src/euler51/src/main.rs b/src/euler51/src/main.rs
index 0beb462..f82733c 100644
--- a/src/euler51/src/main.rs
+++ b/src/euler51/src/main.rs
@@ -1,7 +1,7 @@
 extern crate combination;
 extern crate primes;
 
-use std::process::exit;
+use std::{collections::HashSet, process::exit};
 
 use combination::PositionCombinations;
 use primes::Primes;
@@ -32,18 +32,26 @@ const DIGITS: [u8; 10] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
 
 fn main() {
     let all_primes = Primes::get_between(MIN_VALUE, MAX_VALUE);
+    let mut processed_cases = HashSet::new();
+    let mut primes_matching_pattern = Vec::with_capacity(TARGET_LENGTH);
 
     for pattern in PositionCombinations::new(MIN_LENGTH, MAX_LENGTH, LENGTH) {
-        let mut primes_to_check = all_primes.clone();
+        for prime in &all_primes.vector {
+            primes_matching_pattern.clear();
 
-        while let Some(first) = primes_to_check.pop() {
-            let mut primes_matching_pattern = vec![];
+            let digits = prime.to_digits();
+
+            let case = get_case_string(&digits, &pattern);
+            if processed_cases.contains(&case) {
+                continue;
+            } else {
+                processed_cases.insert(case.clone());
+            }
 
-            let digits = first.to_digits();
             for digit in DIGITS {
                 let could_be_prime =
-                    replace_digits_according_to_pattern_with_digit(&digits, digit, &pattern);
-                if primes_to_check.contains(&could_be_prime) || could_be_prime == first {
+                    replace_digits_with_new_digit_according_to_pattern(&digits, digit, &pattern);
+                if all_primes.contains(&could_be_prime) {
                     primes_matching_pattern.push(could_be_prime);
                 }
             }
@@ -55,7 +63,15 @@ fn main() {
     }
 }
 
-fn replace_digits_according_to_pattern_with_digit(
+fn get_case_string(digits: &[u8], pattern: &[bool]) -> String {
+    digits
+        .iter()
+        .zip(pattern)
+        .map(|(d, b)| if *b { '*' } else { *d as char })
+        .collect()
+}
+
+fn replace_digits_with_new_digit_according_to_pattern(
     prime_as_digits: &[u8],
     new_digit: u8,
     pattern: &[bool],
@@ -86,24 +102,36 @@ trait ToDigits {
 #[allow(clippy::needless_range_loop)]
 impl ToDigits for Int {
     fn to_digits(&self) -> Vec<u8> {
-        let oom = (*self as f64).log10().floor() as i32;
-        let length = oom as usize + 1;
+        let oom = get_order_of_magnitude(*self);
+        let length = oom as usize;
         let mut var = *self;
         let mut result = vec![0; length];
-        for i in 0..length as usize {
-            let power = 10_f64.powi(oom - i as i32);
-            let digit = (var as f64 / power).floor();
+        for i in 0..length {
+            let power = 10_u64.pow(oom - i as u32 - 1);
+            let digit = var / power;
             var -= (digit * power) as Int;
             result[i] = digit as u8;
         }
-        assert_eq!(var, 0);
+        debug_assert_eq!(var, 0);
         result
     }
 }
 
+fn get_order_of_magnitude(x: Int) -> u32 {
+    let mut tmp = 1;
+    let mut oom = 1;
+    while tmp - 1 < x {
+        oom += 1;
+        tmp *= 10;
+    }
+    oom - 1
+}
+
 #[cfg(test)]
 mod test {
-    use crate::{replace_digits_according_to_pattern_with_digit, ToDigits};
+    use crate::{
+        get_order_of_magnitude, replace_digits_with_new_digit_according_to_pattern, ToDigits,
+    };
 
     #[test]
     fn test_num_to_digits() {
@@ -117,7 +145,11 @@ mod test {
         let new_digit = 0;
         let pattern = [false, true, true, true, false, false];
         assert_eq!(
-            replace_digits_according_to_pattern_with_digit(&prime_as_digits, new_digit, &pattern),
+            replace_digits_with_new_digit_according_to_pattern(
+                &prime_as_digits,
+                new_digit,
+                &pattern
+            ),
             500_021
         );
     }
@@ -127,4 +159,15 @@ mod test {
         let num = 37871_u64;
         assert_eq!(vec![3, 7, 8, 7, 1], num.to_digits());
     }
+
+    #[test]
+    fn test_oom() {
+        assert_eq!(get_order_of_magnitude(3), 1);
+        assert_eq!(get_order_of_magnitude(9), 1);
+        assert_eq!(get_order_of_magnitude(10), 2);
+        assert_eq!(get_order_of_magnitude(32), 2);
+        assert_eq!(get_order_of_magnitude(10_000), 5);
+        assert_eq!(get_order_of_magnitude(10_001), 5);
+        assert_eq!(get_order_of_magnitude(37_871), 5);
+    }
 }