speed up proper divisor algorithm (95)

src/euler95/src/main.rs

@@ -23,6 +23,10 @@ fn main() {
     println!("{smallest}");
 }
 
+fn build_proper_divisors(max: usize) -> Vec<Vec<usize>> {
+    todo!()
+}
+
 fn try_build_chain_from_number(
     max: usize,
     mut current: usize,
@@ -34,7 +38,7 @@ fn try_build_chain_from_number(
     loop {
         maybe_chain.push(current);
 
-        let next: usize = get_proper_divisors(current).sum();
+        let next: usize = get_proper_divisors(current).into_iter().sum();
 
         if next > max || next == 0 {
             break;
@@ -55,9 +59,29 @@ fn try_build_chain_from_number(
     }
 }
 
-fn get_proper_divisors(x: usize) -> impl Iterator<Item = usize> {
+fn get_proper_divisors(x: usize) -> Vec<usize> {
+    let mut result = vec![1];
+
     let limit = x / 2 + 1;
-    (1..limit).filter(move |i| x % *i == 0)
+
+    for i in 2..limit {
+        if result.contains(&i) {
+            break;
+        }
+
+        if x % i == 0 {
+            let div_1 = i;
+            let div_2 = x / i;
+            result.push(div_1);
+
+            if div_2 != div_1 {
+                result.push(div_2);
+            }
+        }
+    }
+
+    result.sort_unstable();
+    result
 }
 
 #[cfg(test)]
@@ -72,7 +96,7 @@ mod tests {
     fn proper_divisor(#[case] input: usize, #[case] expected: Vec<usize>) {
         use crate::get_proper_divisors;
 
-        assert_eq!(get_proper_divisors(input).collect::<Vec<_>>(), expected);
+        assert_eq!(get_proper_divisors(input), expected);
     }
 
     #[rstest]