#include <bits/stdc++.h>
using namespace std;
#define ll long long
const ll mod = 1000000007;
const int p1 = 31;
ll modpow(int base, int p) {
if (p == 0) return 1;\
if (p & 2) {
ll tmp = modpow(base, p/2);
return (tmp*tmp)%mod;
}
ll tmp = modpow(base, p-1);
return (tmp*base) % mod;
}
const int maxn = 2000010;
ll preh[maxn];
ll sufh[maxn];
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int N;
string u;
cin >> N >> u;
if (N%2 == 0) {
cout << "NOT POSSIBLE" << endl;
return 0;
}
vector<int> rem; //just push back stuff
int le = (N-1)/2;
ll fh = 0;
ll sh = 0;
for (int i = 0; i < le; i++) {
fh = (fh*p1) + (u[i]-'A'+1);
fh %= mod;
preh[i] = fh;
}
set<int> sols;
preh[le] = preh[le-1]*p1 + (u[le]-'A'+1);
preh[le] %= mod;
ll ofh = fh;
for (int i = le+1; i < N; i++) {
sh = (sh*p1) + (u[i]-'A'+1);
}
if (fh == sh){
rem.push_back(le);
sols.insert(sh);
}
// cout << fh << " - " << sh << endl;
ll cp = 1LL;
//compute suffix hashes
sufh[le] = u[le]-'A'+1;
for (int i = le-1; i >= 0; i--) {
cp = (cp*p1)%mod;
sufh[i] = (sufh[i+1] + (cp*(u[i]-'A'+1)) )%mod;
}
// cout << u.substr(0, le+1) << endl;
// for (int i = 0; i <= le; i++) {
// cout << preh[i] << " " << sufh[i] << endl;
// }
cp = 1LL;
for (int i = le-1; i >= 0; i--) {
//consider meshing these together
cp = (cp*p1)%mod;
ll ch = 0LL;
if (i > 0) {
ch = (ch + preh[i-1]*cp)%mod;
}
ch = (ch + sufh[i+1])%mod;
if (ch == sh) {
rem.push_back(i);
sols.insert(sh);
}
// cout << i << ": current hash: " << ch << endl;
}
//now do the second half of it
//recalculate prefix and suffix hashes
//then we just go through and do exact same thing
fill(preh, preh+maxn, 0);
fill(sufh, sufh+maxn, 0);
sh = ofh; //just flip b/c why not
// cout << "new sh: " << sh << endl;
preh[le] = u[le]-'A'+1;
for (int i = le+1; i < N; i++) {
preh[i] = ((preh[i-1]*p1) + u[i]-'A'+1)%mod;
}
sufh[N-1] = u[N-1]-'A'+1;
cp = 1LL;
for (int i = N-2; i >= 0; i--) {
cp = (cp*p1)%mod;
sufh[i] = (sufh[i+1] + (cp*(u[i]-'A'+1)) )%mod;
}
for (int i = N-1; i > le; i--) {
//consider meshing these together
cp = (cp*p1)%mod;
if (i == N-1) cp = 1LL;
ll ch = 0LL;
if (i > 0) {
ch = (ch + preh[i-1]*cp)%mod;
}
if (i != N-1) ch = (ch + sufh[i+1])%mod;
if (ch == sh) {
rem.push_back(i);
sols.insert(ch);
}
// cout << i << ": current hash: " << ch << endl;
}
///////
///////
///////
if (rem.size() == 0) {
cout << "NOT POSSIBLE" << endl;
return 0;
}
if (sols.size() > 1) {
cout << "NOT UNIQUE" << endl;
return 0;
}
int ind = rem[0];
string ans;
if (ind < le) {
ans = u.substr(le+1);
}
else {
ans = u.substr(0, le);
}
cout << ans << endl;
}
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
2 ms |
376 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
3 ms |
376 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
27 ms |
31652 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
3 ms |
31652 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
