Description
Spring is coming, T_T.
All you know Goldbach conjecture.That is to say, Every even integer greater than 2 can be expressed as the sum of two primes. Today, skywind present a new conjecture: every even integer can be expressed as the difference of two primes. To validate this conjecture, you are asked to write a program.
Input
The first line of input is a number n identified the count of test cases(n<10^4). There is a even number x at the next n lines. The absolute value of x is not greater than 10^6.
Output
For each number x tested, outputs two primes a and b at one line separated with one space where a-b=x. If more than one group can meet it, output the minimum group(of course refers b). If no primes can satisfy it, output 'FAIL'.
Sample Input
3
6
10
20
Sample Output
11 5
13 3
23 3
把一个偶数写成两个质数的差 表打到1e7即可
#include <bits/stdc++.h>
using namespace std;
const int N=1e7+7;
int prime[N/10];
bool vis[N];
int tot=0;
void Er()
{
memset(vis,0,sizeof(vis));
vis[1]=vis[0]=1;
for(int i=2;i<N;i++)
{
if(!vis[i])
{
prime[tot++]=i;
for(int j=i+i;j<N;j+=i)
vis[j]=1;
}
}
}
int main()
{
Er();
// for(int i=0;i<10;i++)
// cout<<prime[i]<<'\n';
int t,n;
scanf("%d",&t);
while(t--)
{
scanf("%d",&n);
int it=lower_bound(prime,prime+tot,n)-prime;
bool f=0;
for(int i=it;i<tot;i++)
{
if(!vis[prime[i]-n])
{
f=1;
cout<<prime[i]<<' '<<prime[i]-n<<'\n';
break;
}
}
if(!f)
cout<<"FAIL"<<'\n';
}
return 0;
}