素数区间

线性筛+二分，特判1

#include <bits/stdc++.h>
#define rep(i,x,n) for(int i=x;i<n;i++)
#define repd(i,x,n) for(int i=x;i<=n;i++)
#define lowbit(x) (x&-x)
using namespace std;
const int N = 1E5+10,PN = N/2;
vector<int> prime;
int nprime[N];
void Euler()
{
	for(int i=2;i<=N;i++)
	{
		if(!nprime[i])
		   nprime[i]=i,prime.push_back(i);
		   
		rep(j,0,prime.size())
		{
			if(prime[j]*i>N||prime[j]>nprime[i])
			   break;
			else 
			   nprime[i*prime[j]]=prime[j];
		}
	}
}
int ask(int x)
{
	int pos=upper_bound(prime.begin(),prime.end(),x)-prime.begin();
	return prime[pos]-prime[pos-1]-1;
}
int main()
{
	Euler();
    
	int t,x;
	cin>>t;
	repd(i,1,t)
	{
		cin>>x;
		if(x==1||nprime[x]==x) cout<<0<<endl;
		else cout<<ask(x)<<endl;
	}
	return 0;
}

标签：prime,cin,int,nprime,pos,素数,区间,Euler
来源： https://www.cnblogs.com/BeautifulWater/p/15228831.html