test/yuki2855.test.cpp

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Last update: 2024-05-17 14:55:36+09:00
Problem: https://yukicoder.me/problems/2855
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Code

#define PROBLEM "https://yukicoder.me/problems/2855"

#include "../template.hpp"

#include "../Math/Sieve.hpp"

signed main(){
    int n;cin>>n;
    auto isp=sieve(n);
    vector<ll> ps;
    for(int i=2;i<=n;i++)if(isp[i])ps.push_back(i);
    set<ll> r2;
    rep(i,(int)ps.size()) r2.insert(ps[i]*ps[i]);
    int ans=0;
    for(auto x:ps){
        if(r2.count(2+x)){
            ans+=2;
            if(x==2) ans--;
        }
    }
    cout<<ans<<endl;
    return 0;
}

#line 1 "test/yuki2855.test.cpp"
#define PROBLEM "https://yukicoder.me/problems/2855"

#line 1 "template.hpp"
#include<bits/stdc++.h>
using namespace std;
#define ALL(x) begin(x),end(x)
#define rep(i,n) for(int i=0;i<(n);i++)
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define mod 1000000007
using ll=long long;
const int INF=1000000000;
const ll LINF=1001002003004005006ll;
int dx[]={1,0,-1,0},dy[]={0,1,0,-1};
// ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}

struct IOSetup{
    IOSetup(){
        cin.tie(0);
        ios::sync_with_stdio(0);
        cout<<fixed<<setprecision(12);
    }
} iosetup;
 
template<typename T>
ostream &operator<<(ostream &os,const vector<T>&v){
    for(int i=0;i<(int)v.size();i++) os<<v[i]<<(i+1==(int)v.size()?"":" ");
    return os;
}
template<typename T>
istream &operator>>(istream &is,vector<T>&v){
    for(T &x:v)is>>x;
    return is;
}

#line 4 "test/yuki2855.test.cpp"

#line 1 "Math/Sieve.hpp"
vector<bool> sieve(int n){
    vector<bool> ret(n+1,true);
    ret[0]=false;
    if(n>0) ret[1]=false;
    for(int i=2;i*i<=n;i++){
        if(!ret[i]) continue;
        for(int j=i*2;j<=n;j+=i) ret[j]=false;
    }
    return ret;
}
#line 6 "test/yuki2855.test.cpp"

signed main(){
    int n;cin>>n;
    auto isp=sieve(n);
    vector<ll> ps;
    for(int i=2;i<=n;i++)if(isp[i])ps.push_back(i);
    set<ll> r2;
    rep(i,(int)ps.size()) r2.insert(ps[i]*ps[i]);
    int ans=0;
    for(auto x:ps){
        if(r2.count(2+x)){
            ans+=2;
            if(x==2) ans--;
        }
    }
    cout<<ans<<endl;
    return 0;
}