We are given N equations, a target, a list of operators and a list of integers.
- Each equation is of the form OPERAND1 OPERATOR OPERAND2 = RESULT.
- We need to fill in these equations with the operands, operators and the results such that the result of the last equation is equal to the target.
- We are also given a list of operands and operators (there can be repeats in these lists). Each of these can be used exactly once.
- We can also use results of equations as operands in subsequent equations. Each result can be used exactly once.
- Operators are + for addition, - for subtraction, * for multiplication and / for division.
