## Postfix to infix with unary/binary operators

问题 I am trying to make a converter from postfix to infix notation and need some help. There is already a question about infix-to-postfix conversion, which gives an example I am failing to convert back. (Note: a minus sign is missing there!) The following is the output of my converter, where the 1st "column" is postfix input, the 2nd is my infix output, and the 3rd is what I probably should get(?): 2 - = - 2 =? - 2 true 1 + 2 + = + 1 + 2 =? + 1 + 2 true 1 + 2 + + = + (+ 1 + 2) =? + 1 + + 2 false