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View the Project on GitHub mugen1337/procon
#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; }