Ehrlich sieve method [template]

sieve of prime numbers

General idea:

Enumerate each number, sieve out (b[i]=1;) its multiples and use it as a prime number, the multiples are no longer enumerated, so that all prime numbers are left after sieving.

Note that this algorithm has the disadvantage that it is not as time-complex as a linear sieve.

#include<iostream>
#include<cstdio>
#define MAXX 1000

MAXX can be larger, here is 1000 for convenience.

using namespace std;
bool b[MAXX];
int main()
{
    for(int i=2;i<=MAXX/2+1;i++)
    {
        if(b[i]==0)
        {
            for(int j=2;;j++)

The point! ! ! Don't start enumerating from 1, that will filter out all numbers that are not 1. 1 There should be a special judgment.

            {
                if(j>MAXX/i) break;
                b[i*j]=1;
            }
        }
    }
    for(int i=1;i<=MAXX;i++)
        if(b[i]==0) cout<<i<<endl;
}

If the definition of MAXX is relatively large, it is recommended to use freopen file output, otherwise it may not be possible to view all prime numbers.