Proposal: BinaryHeap::remove

[SkiFire13]

@BadAtUsernames

for i in (prime / 4)..(3 * prime / 4) {
    heap.retain(|&x| x != i);
    // let mut j = 0;
    // while heap.as_slice()[j] != i { j += 1; }
    // heap.remove(j);
}

This is just:

let range = (prime / 4)..(3 * prime / 4);
heap.retain(|x| range.contains(x));

which is better than both solutions since it's O(n) rather than O(n²)