BFS 70pts TLE求调

#include <bits/stdc++.h>
using namespace std;
struct node {
    int x, y;
};
int cnt;
int dx[5] = {0, -1, 0, 1, 0},
    dy[5] = {0, 0, 1, 0, -1};
char ch[1010][1010];
bool vis[1010][1010];
int main () {
    int n, m;
    cin >> n >> m;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            cin >> ch[i][j];
        }
    }
    while (m--) {
        int x, y;
        queue <node> q;
        cin >> x >> y;
        q.push({x, y});
        cnt = 1;
        memset(vis, 0, sizeof(vis));
        vis[x][y] = true;
        while (!q.empty()) {
            node cur = q.front();
            q.pop();
            for (int i = 1; i <= 4; i++) {
                int nx = cur.x + dx[i], ny = cur.y + dy[i];
                if (nx && nx <= n && ny && ny <= n && ch[nx][ny] != ch[cur.x][cur.y] && !vis[nx][ny]) {
                    q.push({nx, ny});
                    vis[nx][ny] = true;
                    cnt++;
                }
            }
        }
        cout << cnt << endl;
    }
}