exercism-ts/sieve/sieve.ts

enum State {
    Maybe = 0,
    Prime,
    NotPrime,
}

export function primes(limit: number): number[] {
    const all: number[] = Array(limit + 1).fill(State.Maybe);
    all[0] = State.NotPrime;
    all[1] = State.NotPrime;
    for (let i = 2; i <= limit; i++) {
        if (all[i] === State.NotPrime) {
            continue;
        }
        all[i] = State.Prime;
        for (let j = 2; j <= limit / i; j++) {
            all[i * j] = State.NotPrime;
        }
    }
    const res: number[] = [];
    let property: keyof typeof all;
    for (property in all) {
        if (all[property] === State.Prime) {
            res.push(Number(property));
        }
    }
    return res;
}