java - 后缀数字或字母连接的中缀

Question

正在研究将中缀表示法转换为后缀的程序。我让它适用于大多数情况，除非需要字符连接。例如，如果我传入一串数字 (1002+304)，它会输出 1、0、0、2、3、0、4、+ 而不是 1002、304、+。

 import java.util.*;


 public class InfixToPostfix {

     private Deque<String> postfix; // Used as a queue of String


     private static boolean isOperator(char op)
     {
         if(op=='+'||op=='-'||op=='*'||op=='/'||op=='^'
                 ||op=='('||op==')')
         {
             return true;
         }
         return false;
     }

     private static boolean lowerEqualPrec(char op1, char op2)
     {
         boolean flag = false;
         if(op1=='+'|| op1=='-')
         {
             if(op2=='+'||op2=='-'||op2=='*'||op2=='/'||op2=='^')
             {
                 flag= true;
             }
         }else if(op1=='*' || op1=='/')
         {
             if(op2=='*'||op2=='/'||op2=='^')
             {
                 flag= true;
             }
         }else if(op1=='^')
         {
             flag= false;
         }else if(op1=='(')
         {
             flag= false;
         }
         return flag;
     }

     public InfixToPostfix(String infix)
     {
         for(int i=0; i<infix.length(); i++)
         {
             if(infix.length() ==0 || infix.charAt(0)==')' ||
                     infix.charAt(i)=='&' || infix.charAt(infix.length()-1)=='(')
             {
                 throw new IllegalArgumentException();
             }
         }

         postfix = new LinkedList<String>();
         Stack<Character> stack = new Stack<Character>();
         Character ch;
         String digits="";
         String letters = "";


         for(int i=0; i<infix.length(); i++)
         {
             ch=infix.charAt(i);
             if(ch == ' ')
             {
                 //do nothing   
             }

             if(Character.isDigit(ch))
             {

                 digits=""+ch;
                 if(i+1 >= infix.length() || !Character.isDigit(infix.charAt(i+1)))
                 {
                     digits=digits+"";
                 }
                 postfix.add(digits);


             }
             if(Character.isLetter(ch))
             {
                 letters=ch+"";

                 postfix.add(letters);

             }

             if(isOperator(ch))
             {
                 if(ch == ')')
                 {

                     if(!stack.isEmpty() && stack.peek() != '(')
                     {
                         postfix.add(""+stack.pop());
                         if(!stack.isEmpty())
                         {
                             stack.pop();
                         }
                     }
                 }

                 else
                 {

                     if(!stack.isEmpty() && !lowerEqualPrec(ch, stack.peek()))
                     {
                         stack.push(ch);
                     }

                     else
                     {
                         while(!stack.isEmpty() && lowerEqualPrec(ch, stack.peek()))
                         {
                             char pop = stack.pop();
                             if(ch!='(')
                             {
                                 postfix.add(pop+"");
                             }
                         }

                         stack.push(ch);
                     }
                 }
             }
         }
         while(!stack.isEmpty()&&stack.peek()!='(')
         {
             postfix.add(stack.pop()+"");
         }
         System.out.println(postfix);
     }

     public Iterator<String> iterator()
     {
         return new PostfixIterator(postfix) ;
     }

     public static void main(String[] args)
     {
         InfixToPostfix test = new InfixToPostfix("1002+304");
     }

 }

Answer 1

对于后缀转换

public static String postfixConversion(String input) {

        int i;
        String postfix = "";

        Stack<Character> stack = new Stack<Character>();

        for (i = 0; i < input.length(); i++) {
                while (input.charAt(i) == ' ') {
                        ++i;
                }

                if (Character.isDigit(input.charAt(i))) { 
                                postfix += input.charAt(i);

                                //if (!Character.isDigit(input.charAt(i+1))) { 
                                       postfix += ' ';
                                //}
                }

                else if (precedenceLevel(input.charAt(i)) != 0) {
                        while ((!stack.isEmpty()) && (precedenceLevel(stack.peek()) >= precedenceLevel(input.charAt(i))) && (stack.peek() != '(')) {
                                postfix += stack.peek();
                                postfix += ' ';
                                stack.pop();
                        }

                        stack.push(input.charAt(i));
                }

                else if (input.charAt(i) == '(') {
                        stack.push(input.charAt(i));
                }

                else if (input.charAt(i) == ')') {
                        while (!stack.isEmpty() && stack.peek() != '(') {
                                postfix += stack.peek();
                                stack.pop();
                        }

                        stack.pop();
                }
        }

        while (!stack.isEmpty()) {
                postfix += stack.peek();
                postfix += ' ';
        }

        return postfix;

}