Submission #998622

#	Time	Username	Problem	Language	Result	Execution time	Memory
998622		kirilchay	Three Friends (BOI14_friends)	C++17	35 / 100	42 ms	35572 KiB

friends

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define pb push_back
const ll MOD=1e9+7;
const ll L=79;
const ll N =2e6+7;
ll h[N+2],hd[N+2];
int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    ll n;
    cin >> n;

    string s ;
    cin >> s;
    h[0]=1;
    for(ll i=1;i<=N;i++)
    {
        h[i]=(h[i-1]*L)%MOD;
    }
hd[0]=0;
    for(ll i=1;i<=n;i++)
    {
        hd[i]=(((s[i-1]*h[i-1])%MOD)+hd[i-1])%MOD;
    }
    ll sm = 0;
    string ss;
    for(ll i=1;i<=n && sm < 2;i++)
    {
        if(i<=n/2+1){
                ll a=1, b=i-1, c=n/2+2, d=n/2+i;
                ll a2=i+1, b2=n/2+1, c2=n/2+1+i, d2=n;
            if((((hd[b]-hd[a-1]+MOD)%MOD)*h[N-a])%MOD==(((hd[d]-hd[c-1]+MOD)%MOD)*h[N-c])%MOD &&
               (((hd[b2]-hd[a2-1]+MOD)%MOD)*h[N-a2])%MOD==(((hd[d2]-hd[c2-1]+MOD)%MOD)*h[N-c2])%MOD) {sm++;ss=s.substr(n/2+1,n/2);}
        }
        else{
            ll a=1, b=i-(n/2+1), c=n/2+1, d=n/2+(i-(n/2+1));
                ll a2=i-(n/2+1)+1, b2=n/2, c2=n/2+(i-(n/2+1))+2, d2=n;
            if((((hd[b]-hd[a-1]+MOD)%MOD)*h[N-a])%MOD==(((hd[d]-hd[c-1]+MOD)%MOD)*h[N-c])%MOD &&
               (((hd[b2]-hd[a2-1]+MOD)%MOD)*h[N-a2])%MOD==(((hd[d2]-hd[c2-1]+MOD)%MOD)*h[N-c2])%MOD) {sm++;ss=s.substr(0,n/2);}
        }
    }
    if(sm==0)cout<<"NOT POSSIBLE";
    else if(s[0]!=s[1] && sm>1)cout<<"NOT UNIQUE";
    else cout<<ss;

    return 0;
}

• Subtask 1: 35 / 35
• Subtask 2: 0 / 65