模板——区间筛法

原博文http://www.cnblogs.com/nowandforever/p/4515612.html

/************************************************
* Author        :Powatr
* Created Time  :2015-8-17 8:56:45
* File Name     :区间筛法.cpp
 ************************************************/

#include <cstdio>
#include <algorithm>
#include <iostream>
#include <sstream>
#include <cstring>
#include <cmath>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <list>
#include <map>
#include <set>
#include <bitset>
#include <cstdlib>
#include <ctime>
using namespace std;

#define lson l, mid, rt << 1
#define rson mid + 1, r, rt << 1 | 1
typedef long long ll;
const int MAXN = 1e5 + 10;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;

bool is_prime_small[MAXN];
bool is_prime[MAXN];
ll prime[MAXN];
ll cout1;

void segment_sieve (ll a, ll b)
{
    for(ll i = 0 ; i*i < b; i++) is_prime_small[i] = true;
    for(ll i = 0 ; i < b - a; i++) is_prime[i] = true;
    for(ll i = 2; i*i < b; i++){
        if(is_prime_small[i]){
            for(ll j = 2*i; j *j < b; j+=i) is_prime_small[j] = false;
            for(ll j = max(1ll*2, (a+i-1)/i*i); j < b; j+=i) is_prime[j-a] = false;
        }
    }
    for(ll i = 0; i < b - a; i++){
        if(is_prime[i]) prime[++cout1] = i+a;
    }
}

int main(){
    ll a, b;
    while(~scanf("%I64d%I64d", &a, &b)){
    cout1 = 0;
    memset(prime, 0, sizeof(prime));
    segment_sieve(a, b);
    printf("%I64d\n", cout1);
    }
    return 0;
}