素数筛选（模板）

1 const int N=1e6+11; 2 int p[N],pr[N],cnt; 3 void init() 4 { 5 for(int i=2;i<N;i++) 6 { 7 if(!p[i]) pr[++cnt]=i; 8 for(int j=1;j<=cnt&&i*pr[j]<N;j++) 9 { 10 p[i*pr[j]]=1; 11 if(i%pr[j]==0) break; 12 } 13 } 14 }

[模板]素数筛选 1 #include <stdio.h> 2 3 int main() 4 { 5 int i,j,a[505]={0}; 6 for(i=1;i<=500;i++) 7 a[i]=1; 8 for(i=2;i<=500;i++) 9 if(a[i]) 10 for(j=i+i;j<=500;j+=i) 11 a[j]=0; 12 for(i=2;i<=500;i++) 13 if(a[i]) 14 printf("%d ",i);

题目链接: http://acm.hdu.edu.cn/showproblem.php?pid=5407 解题思路: 官方题解: The problem is just to calculate g(N) =\ LCM(C(N,0), C(N,1), ..., C(N, N))g(N) = LCM(C(N,0),C(N,1),...,C(N,N)). Introducing function f(n) =\ LCM(1, 2, ..., n)f(n) = LCM(1,2,...,n), the

题目链接:传送门 题目: Prime Distance Time Limit: 1000MS Memory Limit: 65536K Total Submissions: 24073 Accepted: 6306 Description The branch of mathematics called number theory is about properties of numbers. One of the areas that has captured the interest of

1 #include <cstdio> 2 #include <cstring> 3 #include <algorithm> 4 5 using namespace std; 6 7 int prim[3000000]={2,3,5}; 8 //素数是分为基本素数{2,3}.阳素数{6N+1,N>=1}形式的.阴素数{6N-1,N>=1}形式的 9 //为了代码的好写,在这里这样写的 : 10 //数除了{2,3,5}为素数,其他的数可以写成6N,6N+1

首先,在谈到素数筛选法时,先涉及几个小知识点. 1.一个数是否为质数的判定. 质数,只有1和其本身才是其约数,所以我们判定一个数是否为质数,只需要判定2~(N - 1)中是否存在其约数即可,此种方法的时间复杂度为O(N),随着N的增加,效率依然很慢.这里有个O()的方法:对于一个合数,其必用一个约数(除1外)小于等于其平方根(可用反证法证明),所以我们只需要判断2-之间的数即可. bool is_prime(int num) { const int border = sqrt(num); for

Sieve of Eratosthenes (素数筛选算法) Given a number n, print all primes smaller than or equal to n. It is also given that n is a small number. For example, if n is 10, the output should be “2, 3, 5, 7″. If n is 20, the output should be “2, 3, 5, 7, 11, 13,

题意:输入一个数判断是不是素数,并规定2不是素数. 析:一看就很简单吧,用素数筛选法,注意的是结束条件是n<0,一开始被坑了... 不说了,直接上代码: #include <iostream> #include <cstdio> #include <cstring> #include <cmath> using namespace std; typedef long long LL; const int maxn = 16000 + 10; int p

http://lightoj.com/volume_showproblem.php?problem=1341 Aladdin and the Flying Carpet Time Limit:3000MS     Memory Limit:32768KB     64bit IO Format:%lld & %llu Submit Status Practice LightOJ 1341 Description It's said that Aladdin had to solve seven