Submission #938314

#	Time	Username	Problem	Language	Result	Execution time	Memory
938314		UmairAhmadMirza	Three Friends (BOI14_friends)	C++17	100 / 100	110 ms	64052 KiB

friends

#include <bits/stdc++.h>
using namespace std;
#define int long long
int const N=3e6+5;
int const mod=1e9+9;
int const base=727;
int Hash[N];
int pw[N];
int n;
string s;
void pre(){
  pw[0]=1;
  for(int i=1;i<N;i++)
    pw[i]=(pw[i-1]*base)%mod;
}
void make_Hash(){
  for(int i=1;i<=n;i++)
    Hash[i]=(((Hash[i-1]*base)%mod)+s[i-1])%mod;
}
int compute_Hash(int l,int r){
  return ((Hash[r] - ((Hash[l]*pw[r-l])%mod) )+mod)%mod;
}
int org_Hash1(int e){
  if(e>n/2)
    return Hash[n/2];
  int h=(Hash[e-1]*pw[((n/2)+1)-e])%mod;
  h+=compute_Hash(e,(n/2)+1);
  h%=mod;
  return h;
}
int org_Hash2(int e){
  if(e<=(n/2)+1)
    return compute_Hash((n/2)+1,n);
  int h=(compute_Hash((n/2),e-1)*pw[n-e])%mod;
  h+=compute_Hash(e,n);
  h%=mod;
  return h;
}
string make_str(int p){
  string st="";
  int sz=0;
  int i=0;
  while(i<=n && sz<(n/2)){
    i++;
    if(i==p)
      continue;
    st+=s[i-1];
    sz++;
  }
  return st;
}
signed main() 
{
  cin>>n;
  cin>>s;
  if(n%2==0){
    cout<<"NOT POSSIBLE\n";
    return 0;
  }
  pre();
  make_Hash();
  int rem=0;
  vector<int> rm;
  int cnt=0;
  for(int i=1;i<=n;i++){
    if(org_Hash1(i)==org_Hash2(i)){
      rem=i;
      rm.push_back(i);
      cnt++;
    }
  }
  if(cnt==0)
    cout<<"NOT POSSIBLE"<<endl;
  else if(cnt>1 && make_str(rm[0])!=make_str(rm[1]))
    cout<<"NOT UNIQUE"<<endl;
  else
    cout<<make_str(rem)<<endl;
  return 0;
}

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