Simplify by eliminating sieve

rust/prime-factors/Cargo.toml

@@ -2,6 +2,3 @@
 edition = "2021"
 name = "prime_factors"
 version = "1.1.0"
-
-[dependencies]
-bit-set = "0.8.0"

rust/prime-factors/src/lib.rs

@@ -1,17 +1,9 @@
-use ::bit_set::BitSet;
-
 pub fn factors(n: u64) -> Vec<u64> {
     let n = n
         .try_into()
         .expect("usize is not large enough to factor a u64");
     let bound = isqrt(n);
 
-    let mut not_primes = {
-        // We need to be able to store any integer up to and including the bound.
-        let capacity = bound + 1;
-        BitSet::with_capacity(capacity)
-    };
-
     let mut factors = {
         // Worst case number of factors is a power of 2, number of
         // factors will be the number of bits needed to represent
@@ -22,9 +14,6 @@ pub fn factors(n: u64) -> Vec<u64> {
 
     let mut reduced = n;
     'outer: for i in 2..=bound {
-        if not_primes.contains(i) {
-            continue;
-        }
         while reduced % i == 0 {
             {
                 let i = i
@@ -39,11 +28,6 @@ pub fn factors(n: u64) -> Vec<u64> {
                 break 'outer;
             }
         }
-        for j in (i * i..=bound).step_by(i) {
-            // Ensure we allocated enough capacity for all non-primes.
-            assert!(j < not_primes.capacity());
-            not_primes.insert(j);
-        }
     }
 
     if reduced > 1 {