Question

大家好我在这里有一个中缀到postfix转换器。正在转换

4 - 9 * 11 + 155 * ( 21 - 17 )/ 3

到

4 9 11 155 21 17 3 - * + * -

所以非常接近。这是正确的表达更短。有什么想法吗？

public class ExpressionTools {
    static MyStack<String> operatorStack=new MyStack<String>();
    public static String infixToPostfix(String infix)throws Exception{
     Scanner tokenizer = new Scanner (infix);
        System.out.println("hi");
        String postFixExpression="";
        while (tokenizer.hasNext()){

            String temp=tokenizer.next();
            if(temp.charAt(0)>=48&&temp.charAt(0)<=57){
                for(int i=0; i<temp.length(); i++){
                    if(!Character.isDigit(temp.charAt(i))){
                        throw new PostFixException("Invalid expression"+temp);
                }
                }
                postFixExpression+=temp+" ";
            }

            else if(temp.equals('(')){
                operatorStack.push(temp);
            }
            else if(temp.equals("*")||temp.equals("+")||temp.equals("-")||temp.equals("/")){
                if(!operatorStack.isEmpty()){
                    while(operatorStack.isEmpty()&&operatorStack.peek().equals("*")||operatorStack.isEmpty()&&operatorStack.peek().equals("/")){
                        postFixExpression+=operatorStack.pop()+" ";

                    }
                }
                operatorStack.push(temp);
            }
            else if(temp.equals(")")){
                while(!operatorStack.isEmpty()){
                    if(!operatorStack.peek().equals("(")){
                        postFixExpression+=operatorStack.pop()+" ";
                    }
                    else{
                        operatorStack.pop();
                        break;
                    }

                }
            }
            System.out.println(postFixExpression);
        }


            while(!operatorStack.isEmpty()){
                postFixExpression+=operatorStack.pop()+" ";
            }



    System.out.println("final postfix");
    System.out.println(postFixExpression);
    return postFixExpression;
}

Answer 1

这里有几个问题。

operatorStack.isEmpty()&&operatorStack.peek().equals("*")永远不会成真。
operatorStack.isEmpty()&&operatorStack.peek().equals("/")永远不会成真。
else if(temp.equals('(')){应为else if(temp.equals("(")){。
您的标记生成器不会将)与/分开。您需要在)之后添加空格，或者使用更好的标记器。

中缀到postifx转换器

1 个答案: