真的看不出哪错了，求帮

#include <bits/stdc++.h>

using namespace std;

const int N = 100;

pair<int, int >st, ed;

int n;

int vis[N][N] = { 0 };

char a[N][N];

struct node {
    int x, y, cnt;
};

queue<node>q;

int dy[] = { -1,0,1,0 };
int dx[] = { 0,1,0,-1 };

int bfs(int x, int y, int cnt) {
    q.push(node{ x,y,cnt });
    vis[x][y] = 1;
    while (!q.empty()) {
        node u = q.front();
        if (ed.first == u.x && ed.second == u.y) return u.cnt;
        q.pop();
        int x = u.x, y = u.y;
        for (int i = 0; i < 4; i++) {
            int tx = x + dx[i];
            int ty = y + dy[i];
            if (tx < 0 || tx > n || ty < 0 || ty > n) continue;
            if (vis[tx][ty] || a[tx][ty] == '1') continue;

            vis[tx][ty] = 1;
            q.push(node{ tx ,ty ,cnt + 1 });
        }
    }
    return -1;
}

int main() {
    cin >> n;
    for (int i = 1; i <= n; i++) {
        scanf("%s", a[i]+1);
    }
    cin >> st.first >> st.second >> ed.first >> ed.second;
    cout << bfs(st.first, st.second, 0) << endl;
    //system("pause");
    return 0;
}