28分，求调

#include <iostream>
#include <queue>
using namespace std;

int dx[5]={0, 0, 0, -1, 1};
int dy[5]={0, 1, -1, 0, 0};
int times[505][505];
bool vis[505][505];

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

void bfs()
{
    queue<node> q;
    q.push((node){0, 0, 0});
    vis[0][0] = true;
    while (! q.empty())
    {
        int nx = q.front().x;
        int ny = q.front().y;
        int nt = q.front().time;
        q.pop();
        for (int i = 1;i <= 4; ++ i)
        {
            int tx = nx + dx[i];
            int ty = ny + dy[i];
            int tt = nt + 1;
            if (! vis[tx][ty] && (times[tx][ty] == 0x7fffffff || tt < times[tx][ty]) && tx >= 0  && ty >= 0)
            {
                if (times[tx][ty] == 0x7fffffff)
                {
                    cout << tt << endl;
                    return;
                }
                vis[tx][ty] = true;
                q.push((node){tt, tx, ty});
            }   
        }
    }
    cout << -1 << endl;
    return;
}

int main()
{
    int m;
    cin >> m;
    for (int i = 0;i < 505; ++ i)
    {
        for (int j = 0;j < 505; ++ j)
        {   
            times[i][j] = 0x7fffffff;
        }   
    }

    for (int i = 1;i <= m; ++ i)
    {
        int x, y, t;
        cin >> x >> y >> t;
        times[x][y] = min(times[x][y], t);
        times[x + 1][y] = min(times[x][y], t);
        times[max(x - 1, 0)][y] = min(times[x][y], t);
        times[x][y + 1] = min(times[x][y], t);
        times[x][max(y - 1, 0)] = min(times[x][y], t);
    }

    bfs();
    return 0;
}