feat: Implemented FixEquation class

[aadityamayankar]

✅ Completed the given task by implementing the FixEquation class
✅ Passing all test cases

Approach

To find the missing digit in one of the numbers in the given equation of the form A * B + C = D , we just have to check which operand has the missing digit ?. Once we know the operand with the missing digit, all we have to do is rearrange the equation, if need be, and check the difference between the missing digit operand and expected result of the evaluation of the equation.

Implementation

• Split the input string based on empty spaces and filter out the operands
• Find the missing digit operand from all the operands
• Reorder (if need be) and evaluate the expected result
• Check if the missing digit operand is valid with respect to the expected result and return the digit in place of ? from the expected result.