Math — Fraction to Recurring Decimal

solve(numerator, denominator) — return the fraction as a decimal string. If the
decimal part repeats, enclose the repeating digits in parentheses. The denominator is never 0
and the values fit in a signed 32-bit integer.

Do long division by hand. The remainder after each step fully determines the digits to come,
so a repeated remainder means a repeating decimal. Store, in a map, the position in the
output where each remainder first appeared; when one shows up again, insert ( at its stored
position and append ).

Handle the sign separately (a negative result needs exactly one of the two inputs negative,
and 0 is never "-0").

Examples

solve(1, 2)      → "0.5"
solve(2, 1)      → "2"
solve(4, 333)    → "0.(012)"
solve(1, 6)      → "0.1(6)"
solve(-50, 8)    → "-6.25"