[tx1988]

今天老师让用 Sieve of Eratosthenes 这个算法去求出所有的prime numbers。 比如你input 50， 这个方程就会return 所有的prime number。 老师给了指导：
1. Create the list {2, 3, 4, . . . , N}.
2. Set p = 2, the smallest prime number.
3. Delete all multiples of p that are ≤ N.
4. Replace p with the first number of the remaining list that is ≥ p; this number is the next largest prime ≤ N.
5. Repeat steps 3 and 4 until p2 > N.
It is straightforward to check that all the remaining numbers on the list are prime.

也就是先创建一个array，然后从p=2开始，将所有能整除p的数去掉，但是怎么在已经建立好的array里去掉某一项？我是第一次接触这个，能给能给个示范怎么编这个程序？