prime-factors

rust/prime-factors/src/lib.rs

@@ -1,3 +1,32 @@
-pub fn factors(n: u64) -> Vec<u64> {
-    todo!("This should calculate the prime factors of {n}")
+pub trait PrimeCollector {
+    fn get_counted(&mut self, prime: u64) -> Vec<u64>;
+}
+
+impl PrimeCollector for u64 {
+    fn get_counted(&mut self, prime: u64) -> Vec<u64> {
+        let mut res: Vec<_> = Vec::new();
+        while 0 == *self % prime {
+            *self /= prime;
+            res.push(prime);
+        }
+        res
+    }
+}
+
+pub fn factors(n: u64) -> Vec<u64> {
+    let mut res: Vec<_> = Vec::new();
+
+    let mut n_remained = n;
+    let mut i = 2;
+    while i * i <= n_remained {
+        if n_remained % i == 0 {
+            res.extend(n_remained.get_counted(i));
+        }
+        i += 1;
+    }
+
+    if n_remained > 1 {
+        res.push(n_remained);
+    }
+    res
 }