[leedcode 204] Count Primes

Description:

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

public class Solution {
    public int countPrimes(int n) {
        //筛选法，将坐标为1的倍数均置为0
        if(n<=2)return 0;
        int temp[]=new int[n];
        for(int i=2;i<n;i++){
            temp[i]=1;
        }
        for(int i=2;i<n;i++){
            if(temp[i]==0) continue;
            else{
                for(int j=i+i;j<n;j=j+i)
                    temp[j]=0;
            }
        }
        int res=0;
        for(int i=2;i<n;i++){
            if(temp[i]!=0)res++;
        }
        return res;
    }
}