LeetCode--No.204--Count Primes

Description:

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

Credits:

Special thanks to @mithmatt for adding this problem and creating all test cases.

不敢说是自己的思路。
我发现我刷easy时现在的问题时，不敢提空间复杂度。

记得用各种东西来存数据啊啊啊啊！！问题会简单很多啊啊啊！！

public class Solution {
    public int countPrimes(int n) {
        int[] isPrime = new int[n];
        if (n<=2)
            return 0;
        for(int i = 0; i < n; i++)
            isPrime[i] = 1;
        for(int i = 2; i < n; i++){
            int num = i*2;
            while(num < n){
                isPrime[num] = 0;
                num += i;
            }
        }
        int count = 0;
        for(int i = 2; i < n; i++){
            if (isPrime[i] == 1)
                count++;
        }
        return count;
    }
}