1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
| #include <iostream>
using namespace std;
int n;
unsigned long long hs[2000009], pw[2000009];
string s;
unsigned long long Hash(int l, int r) {
return hs[r] - hs[l - 1] * pw[r - l + 1];
}
signed main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
cin >> n >> s;
if ((s.size() & 1) == 0) {
cout << "NOT POSSIBLE";
return 0;
}
pw[0] = 1;
for (int i = 1; i <= n; i++) {
pw[i] = pw[i - 1] * 38734667;
hs[i] = hs[i - 1] * 38734667 + s[i - 1] - 'A';
}
int cnt = 0;
unsigned long long hashs = 1;
string str;
for (int i = 0; i < n; i++) {
unsigned long long h1, h2;
if (i == 0) {
h1 = Hash(2, (n >> 1) + 1), h2 = Hash((n >> 1) + 2, n);
} else if (i > (n >> 1)) {
h1 = Hash(1, (n >> 1)), h2 = Hash((n >> 1) + 1, i) * pw[n - (i + 2) + 1] + Hash(i + 2, n);
} else if (i == (n >> 1)) {
h1 = Hash(1, (n >> 1)), h2 = Hash((n >> 1) + 2, n);
} else {
h1 = Hash(1, i) * pw[(n >> 1) + 1 - (i + 2) + 1] + Hash(i + 2, (n >> 1) + 1), h2 = Hash((n >> 1) + 2, n);
}
if (h1 == h2) {
if (h1 == hashs) {
continue;
}
string s;
if (i == 0) {
s = ::s.substr(1, n >> 1);
} else if (i > (n >> 1)) {
s = ::s.substr(0, n >> 1);
} else if (i == (n >> 1)) {
s = ::s.substr(0, n >> 1);
} else {
s = ::s.substr((n >> 1) + 1, n >> 1);
}
cnt += 1;
hashs = h1;
str = s;
if (cnt > 1) {
cout << "NOT UNIQUE";
return 0;
}
}
}
cout << (cnt > 0 ? str : "NOT POSSIBLE");
}
|