이 제출은 이전 버전의 oj.uz에서 채점하였습니다. 현재는 제출 당시와는 다른 서버에서 채점을 하기 때문에, 다시 제출하면 결과가 달라질 수도 있습니다.
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define mp make_pair
#define pb push_back
#define x first
#define y second
#define pii pair<int, int>
#define p3i pair<pii, int>
#define pll pair<ll, ll>
#define p3l pair<pll, ll>
#define lseg L, (L+R)/2, N*2+1
#define rseg (L+R)/2+1, R, N*2+2
#define ub upper_bound
#define lb lower_bound
#define pq priority_queue
#define MN 1000000007
#define fox(k, x) for (int k=0; k<x; ++k)
#define fox1(k, x) for (int k=1; k<=x; ++k)
#define foxr(k, x) for (int k=x-1; k>=0; --k)
#define fox1r(k, x) for (int k=x; k>0; --k)
#define ms multiset
#define flood(x) memset(x, 0x3f3f3f3f, sizeof x)
#define drain(x) memset(x, 0, sizeof x)
#define rng() (rand() >> 3)*rand()
int n, c[2], p=-1, ans, seed=1337, k[2000005], hsh[2000005], hsh2;
string s;
int main(){
//cin.sync_with_stdio(0);
//cin.tie(0);
//cout.sync_with_stdio(0);
//cout.tie(0);
cin >> n >> s;
n=s.size();
if (n%2==0){
cout << "NOT POSSIBLE";
return 0;
}
fox(l, n/2+1){
c[s[l]==s[l+n/2]]++;
}
k[n-1]=1;
foxr(l, n){
hsh[l]=(hsh[l+1]+1LL*s[l]*k[l])%MN;
if (l>0) k[l-1]=(1LL*k[l]*seed)%MN;
//cout << hsh[l] << ' ';
}
//cout << endl;
fox(l, n){
if (l<=n/2)
c[s[l]==s[l+n/2]]--;
else
c[s[l]==s[l-n/2-1]]--;
if (c[0]==0){
// cout << (1LL*hsh2+hsh[l+1])%MN << endl;
if (p!=-1 && (1LL*hsh2+hsh[l+1])%MN!=ans){
cout << "NOT UNIQUE";
return 0;
}
p=l;
ans=(1LL*hsh2+hsh[l+1])%MN;
}
hsh2=(hsh2+1LL*k[l+1]*s[l])%MN;
//cout << c[0] << endl;
if (l<n/2)
c[s[l]==s[l+n/2+1]]++;
else
c[s[l]==s[l-n/2]]++;
}
if (p==-1) cout << "NOT POSSIBLE";
else {
//if (p>=n) while(1);
s.erase(p, 1);
s.erase(0, n/2);
cout << s;
}
return 0;
}
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