0分求助

#include <bits/stdc++.h>
using namespace std;
int n, m,ans = 0;
int dx[] = {-1, 0, 1, 0}; 
int dy[] = {0, 1, 0, -1}; 
char a[1010][1010];
bool vis[1010][1010];//标记某个位置是否走过
void dfs(int x, int y) { //当前在x,y这个位置
    if (x == 1 && y == n) {
        ans++;
        return;
    }
    for (int i = 0; i < 4; i++) {//枚举x,y的4个方位
        int nx = x + dx[i], ny = y + dy[i];//周围的坐标
        if (nx < 1 || nx > n || ny < 1 || ny > n) {
            continue;//越界
        }
        if (vis[nx][ny]) {
            continue;//已经走过了
        }
        if (a[nx][ny] == a[x][y]) {
            continue;//不能走
        }
        vis[nx][ny] = 1;
        dfs(nx, ny);
        vis[nx][ny] = 0;
    }
}
int main() {
    cin >> n >> m;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            cin >> a[i][j];
        }
    }
    while(m--){
        int x,y;
        cin>>x>>y;
        ans = 1;
        dfs(x,y);
        cout<<ans<<endl;
    }
    return 0;
}