curl http://localhost:80/problem2.php -X POST -H Content-Type:application/json --data-binary "{'cells': [4,8,11,18,19], 'distance': 2}"

$data = json_decode(file_get_contents('php://input'));

--data-binary '{"cells": [4,8,11,18,19], "distance": 2}'

var_dump(json_decode('{"cells": [4,8,11,18,19], "distance": 2}'));

print_r($data->cells);

Array
(
    [0] => 4
    [1] => 8
    [2] => 11
    [3] => 18
    [4] => 19
)