Whether the input is encoded as binary or decimal doesn't change whether the time complexity is in PSPACE, NP or P. You need some finite alphabet, and then enco

Whether the input is encoded as binary or decimal doesn't change whether the time complexity is in PSPACE, NP or P. You need some finite alphabet, and then encode the input as a string in this alphabet. The time complexity of an algorithm for SSS is measured by how long it takes (in the worst case) as a function of the length of the input string. As long as you use a positional notation like binary or decimal to encode the integers, the big O of the time complexity will remain the same, and so the exact positional notation doesn't actually matter. The size of the alphabet doesn't matter either. If on the other hand you encode the integers using unary notation, then this can land the problem in P.