01迷宫

#include <bits/stdc++.h>
using namespace std;
char g[1003][1003];
int vis[1003][1003];
int dx[] = {0, 1, 0, -1}, dy[] = {-1, 0, 1, 0}, nx, ny, n, m;
int now, ans[1003][1003];
//“可变长数组”
//ax.clear();
//ax.size();
//ax.push_back(x);
//ax[i]
vector<int> ax, ay; //记录dfs走过的点
void dfs(int x, int y, int flag)
{
    vis[x][y] = flag; //标记当前位置走过了
    now++;            //当前能走到的点多一个
    ax.push_back(x);  //储存dfs走过的路
    ay.push_back(y);
    for (int i = 0; i < 4; i++)
    {
        nx = x + dx[i];
        ny = y + dy[i];
        if (g[x][y] == g[nx][ny])
            continue;
        if (nx && ny && nx <= n && ny <= n)
            if (vis[nx][ny] != flag)
                dfs(nx, ny, flag);
    }
}
int main()
{
    //输入
    cin >> n >> m;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
            cin >> g[i][j];
    //处理每个询问
    memset(vis, 0, sizeof(vis));
    memset(ans, -1, sizeof(ans));
    for (int i = 1; i <= m; i++)
    {
        int x, y;
        cin >> x >> y;
        if (ans[x][y] == -1)
        {
            now = 0;
            dfs(x, y, i);
            //dfs路径上所有点可以走到的点的数量设置为now
            for (int i = 0; i < ax.size(); i++)
                ans[ax[i]][ay[i]] = now;
            ax.clear();
            ay.clear();
        }
        cout << ans[x][y] << endl;
    }
}