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筛选法求素数

2010-04-01 22:44:53| 分类：算法与acm | 标签： |举报 |字号大中小订阅

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const long maxn=1000001;
bool prime[maxn];
//筛选法求素数
//0代表素数，1代表非素数

void primeinit(){
long long i=2,t;
for(i=4;i<maxn;i=i+2)
prime[i]=false;
for(i=3;i<maxn;i=i+2)
{

    if(prime[i])
    {
        t=i*i;
        while(t<maxn)
        {
        prime[t]=false;
        t=t+i;//<<2;//偶数倍不用检测i*i为奇数，故i*i+2i必为奇数
        }

    }

}

}

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