[JZOJ] 5835. Prime

显然的区间筛法

#include<algorithm> 
#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;

typedef long long ll;

ll L,R,k,n;

const int MAXN = 10000005;

int prime[MAXN],tot;
bool isx[MAXN];
void mkprime(){
	for(int i=2;i<=n;i++){
		if(!isx[i]){prime[++tot]=i;}
		for(int j=1;i*prime[j]<=n&&j<=tot;j++){
			int v=prime[j];
			isx[i*v]=1;
			if(i%v==0)break;	
		}
	}
}

bool vis[MAXN];
int main(){
	freopen("prime.in","r",stdin);
	freopen("prime.out","w",stdout);
	cin>>L>>R>>k;
	n=sqrt(R);
	n=min(n,k);
	mkprime();
	for(int i=1;i<=tot;i++){
		int v=prime[i];
		ll cur=1ll*v*(L/v);
		if(cur<L)cur+=v;
		if(cur==v)cur+=v;
		for(;cur<=R;cur+=v)vis[cur-L]=1;	
	}
	ll ans=0;
	int up=R-L,i;
	for(i=0;i<=up;i++){
		if(!vis[i]) ans^=(i+L);
	}
	cout<<ans;
	return 0;
}