Submission #958389

#	Time	Username	Problem	Language	Result	Execution time	Memory
958389		yeediot	Three Friends (BOI14_friends)	C++17	100 / 100	63 ms	37640 KiB

friends

#include<bits/stdc++.h>
using namespace std;
#define int long long
#define F first
#define S second
#define all(x) x.begin(),x.end()
#define pii pair<int,int>
#define pb push_back
#define sz(x) (int)(x.size())
#define chmin(x,y) x=min(x,y)
#define chmax(x,y) x=max(x,y)
#define vi vector<int>
#define vp vector<pii>
#define vvi vector<vi>
#define ykh mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count())
#define __lg(x) 63-__builtin_clzll(x)
#define pow2(x) (1LL<<x)
void __print(int x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifdef local
void setio(){freopen("/Users/iantsai/Library/Mobile Documents/com~apple~CloudDocs/cpp/Empty.md","r",stdin);}
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
void setio(){}
#define debug(x...)
#endif
void setIO(string s) {
    freopen((s + ".in").c_str(), "r", stdin);
    freopen((s + ".out").c_str(), "w", stdout);
}
struct line{
    int a,b;
    int operator()(const int x)const{
        return a*x+b;
    }
};
bool check(line l1,line l2,line l3){
    return (l3.b-l2.b)*(l1.a-l2.a)<=(l2.b-l1.b)*(l2.a-l3.a);
}
const int mod=1e9+7;
const int p=3773;
const int mxn=2e6+5;
int h[mxn],pw[mxn];
int get(int l,int r){
    if(r<l)return 0;
    return (h[r]-h[l-1]*pw[r-l+1]%mod+mod)%mod;
}
signed main(){
    setio();
    ios::sync_with_stdio(0);
    cin.tie(0);cout.tie(0);
    int n;
    cin>>n;
    if(n%2==0){
        cout<<"NOT POSSIBLE\n";
        return 0;
    }
    string s;
    cin>>s;
    s=" "+s;
    pw[0]=1;
    for(int i=1;i<=n;i++){
        pw[i]=pw[i-1]*p%mod;
        h[i]=(h[i-1]*p%mod+(s[i]-'A'+1))%mod;
    }
    pii ans={-1,-1};
    for(int i=1;i<=n;i++){
        if((i<n/2+1 and (get(1,i-1)*pw[n/2-i+1]%mod+get(i+1,n/2+1))%mod==get(n/2+2,n)) or 
          (i>n/2+1 and (get(1,n/2)==(get(n/2+1,i-1)*pw[n-i]+get(i+1,n))%mod)) or (i==n/2+1 and get(1,i-1)==get(i+1,n))){
            pii now;
            if(i<=n/2+1)
                now={n/2+2,n};
            else
                now={1,n/2};
            if(ans.F==-1){
                ans=now;
            }
            else{
                if(get(ans.F,ans.S)!=get(now.F,now.S)){
                    cout<<"NOT UNIQUE\n";
                    return 0;
                }
            }
        }
    }
    if(ans.F==-1){
        cout<<"NOT POSSIBLE\n";
        return 0;
    }
    cout<<s.substr(ans.F,ans.S-ans.F+1)<<'\n';
}
 /*
 input:
 
 */















 

Compilation message (stderr)

friends.cpp: In function 'void setIO(std::string)':
friends.cpp:42:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   42 |     freopen((s + ".in").c_str(), "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
friends.cpp:43:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   43 |     freopen((s + ".out").c_str(), "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 35 / 35
• Subtask 2: 65 / 65