47

src/euler47/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "euler47"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+itertools = "0.14.0"
+primes = { version = "*", path = "../../lib/primes" }
+
+[dev-dependencies]
+rstest = "0.25.0"

src/euler47/src/main.rs

@@ -0,0 +1,76 @@
+use itertools::Itertools;
+use primes::Primes;
+
+const MAX: usize = 1_000_000;
+
+fn main() {
+    let primes = Primes::get_between(2, MAX);
+
+    'outer: for number in 2..MAX {
+        for i in 0..=3 {
+            let factors = factorize_unique(number + i, &primes);
+            if factors.len() != 4 {
+                continue 'outer;
+            }
+        }
+        println!("{number}");
+        break;
+    }
+}
+
+fn factorize(n: usize, primes: &Primes<usize>) -> Vec<usize> {
+    if primes.contains(&n) {
+        return vec![n];
+    }
+
+    let mut remaining = n;
+    let mut result = vec![];
+    'outer: loop {
+        if remaining == 1 {
+            break 'outer;
+        }
+        'inner: for prime in primes.iter().take_while(|p| **p <= remaining) {
+            let remainder = remaining % prime;
+            if remainder == 0 {
+                result.push(prime.to_owned());
+                remaining /= prime;
+                break 'inner;
+            }
+        }
+    }
+    result
+}
+
+fn factorize_unique(n: usize, primes: &Primes<usize>) -> Vec<usize> {
+    factorize(n, primes).into_iter().unique().collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use primes::Primes;
+
+    use crate::{factorize, factorize_unique};
+
+    use rstest::rstest;
+
+    #[rstest]
+    #[case(14, vec![2, 7])]
+    #[case(15, vec![3, 5])]
+    #[case(644, vec![2, 2, 7, 23])]
+    #[case(645, vec![3, 5, 43])]
+    #[case(646, vec![2, 17, 19])]
+    fn factorization(#[case] input: usize, #[case] expected: Vec<usize>) {
+        let primes = Primes::get_between(2, input);
+        let result = factorize(input, &primes);
+        assert_eq!(result, expected);
+    }
+
+    #[rstest]
+    #[case(644, vec![2, 7, 23])]
+    #[case(645, vec![3, 5, 43])]
+    fn factorization_unique(#[case] input: usize, #[case] expected: Vec<usize>) {
+        let primes = Primes::get_between(2, input);
+        let result = factorize_unique(input, &primes);
+        assert_eq!(result, expected);
+    }
+}