rt, 68pts，题目链接

#include <bits/stdc++.h>

using namespace std;

const int dx [] = {0, 1}, dy [] = {1, 0};

int n, ans;
char g [20] [20];
char str [40];
unordered_set <string> uset;

void dfs (int x, int y, int size) { 
	str [size] = g [x] [y];
	
	if (x + 1 == n && y + 1 == n) {
		uset. insert (str);
		return ;
	}
	
	for (int i = 0 ; i < 2; i ++) {
		int x2 = dx [i] + x;
		int y2 = dy [i] + y;
		
		if (x2 >= n || y2 >= n) {
			continue;
		} 
		
		if (x + y >= n && str [2 * n - size - 2] != g [x] [y]) continue;
		
		dfs (x2, y2, size + 1);
	} 
}

int main () {
	cin >> n;
	
	for (int i = 0 ; i < n ; i ++)
		for (int j = 0 ; j < n ; j ++) {
			cin >> g [i] [j];
		}
		
	dfs (0, 0, 0);

	cout << uset. size ();
	return 0; 
}