COJ 1030 素数槽

http://acm.csu.edu.cn/OnlineJudge/problem.php?id=1030

用线性筛素数果然快多了。

 

#include<cstdio>
#include<cstring>
#include<cstdlib>
#define MAXN 1300000
bool is_p[MAXN];void calc()
{for( int i = 1; i < MAXN; i ++)is_p[i] = true;is_p[1] = false;for( int i = 2; i < MAXN; i ++){if( !is_p[i]) continue;for( int j = 2; i * j < MAXN; j ++)is_p[i * j] = false;}
}int main()
{int n, k, cnt;calc();scanf( "%d", &n);while( n --){scanf( "%d", &k);cnt = 0;for( int i = k; !is_p[i]; i ++)cnt ++;for( int i = k; !is_p[i]; i --)cnt ++;printf( "%d\n", cnt);}return 0;
}