bfs90分TLE求调

#include<bits/stdc++.h>
using namespace std;

typedef pair<int, int> pii;
int check[1010][1010] = {0};
int dx[4] = {0, 0, 1, -1};
int dy[4] = {1, -1, 0, 0};
int n = 0;
int a[1010][1010] = {0};
char a_[1010][1010] = {};
int answer[1010][1010] = {0};

void bfs(pii p){
    int ans = 0;
    queue <pii> q;
    vector <pii> ve;
    if(answer[p.first][p.second]){
        return;
    }
    q.push(p);
    ve.push_back(p);
    check[p.first][p.second] = 1;
    while(!q.empty()){
        pii top = q.front();
        for(int i = 0; i < 4; i++){
            if(top.first + dx[i] > 0 && top.first + dx[i] <= n && top.second + dy[i] > 0 && top.second + dy[i] <= n && check[top.first + dx[i]][top.second + dy[i]] == 0 && a[top.first][top.second] ^ a[top.first + dx[i]][top.second + dy[i]]){
                check[top.first + dx[i]][top.second + dy[i]] = 1;
                q.push({top.first + dx[i], top.second + dy[i]});
                ve.push_back({top.first + dx[i], top.second + dy[i]});
            }
        }
        q.pop();
        ans++;
        for(auto l : ve){
            answer[l.first][l.second] = ans;
        }
    }
}

int main(){
    int m = 0;
    cin>>n>>m;
    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= n; j++){
            cin>>a_[i][j];
            if(a_[i][j] == '1') a[i][j] = 1;
        }
    }

    while(m--){
        int x = 0, y = 0;
        cin>>x>>y;
        bfs({x, y});
        printf("%d\n", answer[x][y]);
    }
    return 0;
}