Submission #938215

#	Time	Username	Problem	Language	Result	Execution time	Memory
938215		Faisal_Saqib	Three Friends (BOI14_friends)	C++17	100 / 100	170 ms	34868 KiB

friends

#include <iostream>
#include <set>
using namespace std;
#define ll long long
const ll N=2e6+2;
ll pre[N],pw[N],base=379,mod=1e9+9;
int get(int l,int r)// one base indexing 1<=l<=n
{
    if(r<l)
        return 0;
    return ((pre[r]-(pre[l-1]*pw[r-l+1])%mod)%mod+mod)%mod;
}
int main()
{
  cin.tie(0);
  cout.tie(0);
  ios::sync_with_stdio(0);
    int n;
    cin>>n;
    string s;
    cin>>s;
    pre[0]=0;
    pw[0]=1;
    for(int i=1;i<=n;i++)
        pw[i]=(pw[i-1]*base)%mod;
    for(int i=1;i<=n;i++)
        pre[i]=((pre[i-1]*base)%mod+(s[i-1]-'A'))%mod;
    int posa=-1;
    int pp;
    int len=(n-1)/2;
    for(int i=1;(n%2==1) and i<=n;i++)
    {
        ll fit=0;
        ll sec=0;
        int lf=(i-1);
        if(lf<=len)
        {
            fit=((get(1,i-1)*pw[len-lf])%mod+get(i+1,i+len-lf))%mod;
            sec=get(i+len-lf+1,n);
        }
        else{
            fit=get(1,len);
            sec=((get(len+1,i-1)*pw[n-i])%mod + get(i+1,n))%mod;
        }
        if(fit==sec)
        {
            if(posa==-1)
            {
                pp=i;
                posa=fit;
            }
            else if(posa!=fit)
            {
                posa=-2;
                break;
            }
        }
    }
    if(posa==-1 or n%2!=1)
    {
        cout<<"NOT POSSIBLE\n";
    }
    else if(posa!=-2)
    {
        int j=(pp);
        for(int i=1,p=0;p<len;i++)
        {
            if(i!=j)
            {
                cout<<s[i-1];
                p++;
            }
        }
        cout<<'\n';
    }
    else{
        cout<<"NOT UNIQUE\n";
    }
    return 0;
}

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