grid of digits from 1 to 9. From any cell you may cast a ray in one of eight directions (horizontal, vertical or diagonal) and follow it straight to the edge of the grid.
Along the way, each digit you pass is appended to a number that begins with the starting cell's digit, and every step produces a new number. For instance, if the ray reads 1, 9, 1, it produces 19 and 191 (the lone starting digit does not count).
Over all numbers produced from every cell in every direction, look at the primes greater than 10 and count how many times each one appears. Return the one that appears most often, breaking ties by taking the largest. If there is no such prime, return -1.grid=[[1, 3], [7, 1]] → 71
The rays give 13, 17, 11, 31, 37, 31, 71, 73, 71, 11, 13, 17. All of them are prime; 11, 13, 17, 31 and 71 appear twice each, and the largest of those is 71.
grid=[[2, 4, 6]] → -1
Every number longer than one digit here is even, so there is no prime above 10.
grid=[[5]] → -1
grid=[[1, 3], [7, 1]]
71
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