生成没有二进制树的后缀

Can we generate a postfix format string from an expression without creating a binary tree or AST tree

For example, I have an expression exp = "1 + 2 * 3 * ( 4 - 2 ) + A / B "
and I want to generate a postfix string = "1 2 3 * 4 2 - * + A B / +"