The base of a number system is the number of different values each digit can represent. For example, in base2 (binary), there are 2 values each digit can take: 0 and 1. In base10, a digit can take values 0 through 9, inclusive. Sometimes, it is difficult to determine which base a numerical expression is in. An equation is valid for a given base if all of the digits are less than the base, and the numerical meaning of the equation is correct. For example, "1+1=10" for base10 satisfies the rule that the digits are all less than 10, but 1+1 = 2 in base10, so the equation is not correct for base10.
If we assume that the characters '0''9' represent the values 0  9, and the characters 'A''J' represent the values 10  19, then we can represent numbers with a base up to 20. The equation will be in the following form:
<num>+<num>=<num>
Where each <num> is a String consisting of characters '0''9' and 'A''J', which does not have any extra leading zeros, and is at most 5 digits long.
Given an equation as defined above, you should return which bases in the range of 2 to 20, inclusive, are valid for the equation. Return the bases in a int[] in ascending order.
