Count Primes

 1 int ary[1500005];
 2 class Solution {
 3 public:
 4     int countPrimes(int n) {
 5         int i,j;
 6         memset(ary,0,sizeof(ary));
 7         int m=sqrt(n)+1;
 8         for(i=2;i<m;i++)
 9         {
10             for(j=i;j<=n/i;j++)
11                 ary[i*j]=1;
12         }
13         int tot=0;
14         for(i=2;i<n;i++)
15         {
16             if(ary[i]==0)tot++;
17         }
18         return tot;
19     }
20 };