没输出！找不到原因！！

#include <cstdio>
#include <queue>
#include <algorithm>
#include <cstring>
const int MAXN = 300 + 5, INF = 0x3f3f3f3f;
int time[MAXN][MAXN], d[MAXN][MAXN];
int m;
int dx[4] = {-1, 0, 1, 0};
int dy[4] = {0, -1, 0, 1};
std::queue<std::pair<int, int> > q;
int main()
{
    scanf("%d", &m);
    for (int i = 0; i < MAXN; i++)
        for (int j = 0; j < MAXN; j++)
        {
            time[i][j] = INF;
            d[i][j] = -1;
        }
    for (int i = 0; i < m; i++)
    {
        int x, y, t;
        scanf("%d %d %d", &x, &y, &t);
        time[x][y] = std::min(time[x][y], t);
        for (int j = 0; i < 4; j++)
        {
            int nx = x + dx[i], ny = y + dy[i];
            if (nx >= 0 && ny >= 0)
            {
                time[nx][ny] = std::min(time[nx][ny], t);
            }
        }
    }
    if (time[0][0] == 0)
    {
        printf("%d\n", -1);
        return 0;
    }
    q.push(std::make_pair(0, 0));
    d[0][0] = 0;
    while (q.size())
    {
        int x = q.front().first, y = q.front().second;
        q.pop();
        for (int i = 0; i < 4; i++)
        {
            int nx = x + dx[i], ny = y + dy[i];
            if (nx >= 0 && ny >= 0 && d[nx][ny] == -1 && d[x][y] + 1 < time[nx][ny])
            {
                d[nx][ny] = d[x][y] + 1;
                if (time[nx][ny] == INF)
                {
                    printf("%d\n", d[nx][ny]);
                    return 0;
                }
                q.push(std::make_pair(nx, ny));
            }
        }
    }
    printf("%d\n", -1);
    return 0;
}