安排操作数和运算符来获取数字

Question

I have one given number n, 4 operands a1, a2, a3, a4, and 4 operators +, -, *, / in Java. I need to test if I can arrange operands with operators so that they form a mathematical expression which equals the given number, or at least is closest in value with it. I don't need to use all operands and each operand can be used only once. I am not asking someone to give me code just to explain if it is possible, or if there is some library for this. Thanks.

Answer 1

This is absolutely possible. You have to do all permutations possible for eg there are two operands a,b and only one operator - . In this case possible permutations are ab and ba . If all permutations are done and you can't get the number, there must be a result like number can't be arrived (one of the possible output) from this function.

Here is a recursive program for doing a basic permutation. Your logic should be similar to this.

Here is a solution to execute your prepared expression and get the result