leetcode | Count Primes

Description:

Count the number of prime numbers less than a non-negative number, n.

找出小于n的质数的个数

public class Solution {    public int countPrimes(int n) {        if(n<=2)            return 0;         boolean[] a = new boolean[n];         int count=0;        for(int i=2;i<n;i++)        {            if(!a[i])            {                count++;                for(int j=i;j<n;j+=i)                {                    a[j]=true;                }            }        }        return count;    }}