O(n³)

int dist[N][N];

void floyd()
{
    for (int k = 1; k <= n; k++)
    {
        for (int i = 1; i <= n; i++)
        {
            for (int j = 1; j <= n; j++)
            {
                dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]);
            }
        }
    }
}

for (int i = 1; i <= n; i++)//初始化
{
    for (int j = 1; j <= n; j++)
    {
        if (i != j)
        {
            dist[i][j] = INF;
        }
    }
}