mirror of
https://git.sb/baoshuo/OI-codes.git
synced 2024-12-25 08:11:59 +00:00
70 lines
1.0 KiB
C++
70 lines
1.0 KiB
C++
#include <iostream>
|
|
#include <string>
|
|
#include <unordered_map>
|
|
|
|
using std::cin;
|
|
using std::cout;
|
|
const char endl = '\n';
|
|
|
|
const int N = (18 << 1) + 5;
|
|
|
|
int n;
|
|
long long ans;
|
|
bool vis[N];
|
|
std::string s;
|
|
std::unordered_map<std::string, int> map;
|
|
|
|
void dfs1(int x) {
|
|
if (x == n + 1) {
|
|
std::string s1, s2;
|
|
|
|
for (int i = 1; i <= n; i++) {
|
|
(vis[i] ? s2 : s1).push_back(s[i]);
|
|
}
|
|
|
|
map[s1 + ' ' + s2]++;
|
|
|
|
return;
|
|
}
|
|
|
|
dfs1(x + 1);
|
|
vis[x] = true;
|
|
dfs1(x + 1);
|
|
vis[x] = false;
|
|
}
|
|
|
|
void dfs2(int x) {
|
|
if (x == n * 2 + 1) {
|
|
std::string s1, s2;
|
|
|
|
for (int i = n + n; i > n; i--) {
|
|
(vis[i] ? s2 : s1).push_back(s[i]);
|
|
}
|
|
|
|
ans += map[s1 + ' ' + s2];
|
|
|
|
return;
|
|
}
|
|
|
|
dfs2(x + 1);
|
|
vis[x] = true;
|
|
dfs2(x + 1);
|
|
vis[x] = false;
|
|
}
|
|
|
|
int main() {
|
|
std::ios::sync_with_stdio(false);
|
|
cin.tie(nullptr);
|
|
|
|
cin >> n >> s;
|
|
|
|
s = ' ' + s;
|
|
|
|
dfs1(1);
|
|
dfs2(n + 1);
|
|
|
|
cout << (ans >> 1) << endl;
|
|
|
|
return 0;
|
|
}
|