蒟蒻样例没过, 但是获得了 70pts 求调 (裸bfs)

Code:

#include<iostream>
#include<cstring>
#include<queue>

using namespace std;

const int maxn = 1010;
int n;
string maze[maxn];
int sx, sy, ex, ey;
bool vis[maxn][maxn];
int dx[4] = {0, 1, 0, -1};
int dy[4] = {1, 0, -1, 0};
int ans[maxn][maxn];

#define mp make_pair

bool in(int x, int y) {
    return x >= 1 && x <= n && y >= 1 && y <= n;
}

int bfs() {
    queue<pair<int, int> > q;
    q.push(mp(sx, sy));
    vis[sx][sy] = true;
    while (!q.empty()) {
        pair<int, int> now = q.front();
        q.pop();
        if (now.first == ex && now.second == ey) {
            return ans[ex][ey];
        }
        for (int i = 0;i < 4;i++) {
            int tx = now.first + dx[i];
            int ty = now.second + dy[i];
            if (in(tx, ty) && !vis[tx][ty] && maze[tx][ty] == '0') {
                q.push(mp(tx, ty));
                vis[tx][ty] = true;
                ans[tx][ty] = ans[now.first][now.second] + 1;
            }
        }
    }
    return -1;
}

int main() {
    cin >> n;
    for (int i = 1;i <= n;i++) {
        cin >> maze[i];
    }
    cin >> sx >> sy >> ex >> ey;
    cout << bfs() << endl;
    return 0;
}