[
    {
        "size": [6, 6],
        "difficulty": 3
    },
    {
        "size": [10, 10],
        "difficulty": 3
    },
    {
        "size": [15, 15],
        "difficulty": 3
    },
    {
        "size": [20, 20],
        "difficulty": 3
    }
]