使用Java將中綴表達式轉換爲前綴和後綴表達式

Question

我想製作一個應用程序，將表達式從中綴模式轉換爲後綴和前綴模式。

例如：

綴：A + B * C

後綴：ABC * +

前綴：+ A * BC

我的兩個班想這樣，一類爲後綴轉換和其他類前綴轉換。

此外，我已經寫了堆一類是這樣的：

public class Stack { 

int top = 0; 
int stackSize = 0; 
String[] stack; 

public Stack(int stackSize){ 
    this.stackSize = stackSize; 
    stack = new String[stackSize]; 
} 

public int getTop(){ 
    return top; 
} 

public void push(String arg)throws Exception{ 
    if(top == stackSize){ 
     throw new Exception("Stack is full!"); 
    } 
    else{ 
     this.stack[top++] = arg; 
    } 
} 

public String pop()throws Exception{ 
    if(top == 0){ 
     throw new Exception("Stack is empty"); 
    } 
    else{ 
     return this.stack[--top]; 
    } 
} 

public int stackCount(){ 
    return top++; 
} 
} 

我想這個代碼後綴類：

public class Postfix { 
Stack stack = new Stack(1000); 
char []operators = {'(','*','%','/','+','-',')'}; 
char[] infixExpression; 
public Postfix(String infixExpression){ 
    this.infixExpression = infixExpression.toCharArray(); 
} 

int priority(char operator){ 
    int result = 0; 
    switch(operator){ 
    case '(': 
     result = 1; 
     break; 
    case '*': 
     result = 2; 
     break; 
    case '%': 
     result = 3; 
     break; 
    case '/': 
     result = 4; 
     break; 
    case '+': 
     result = 5; 
     break; 
    case '-': 
     result = 5; 
     break; 
    case ')': 
     result = 7; 
    } 
    return result; 
} 

public String convertToPostfix(){ 
    int priority; 
    String lastData; 
    String exp = ""; 
    for(int i = 0;i<this.infixExpression.length;i++){ 
     priority = priority(this.infixExpression[i]); 
     if(priority == 0){ 
      exp += this.infixExpression[i]; 
     } 
     else if(priority == 1){ 
      try { 
       stack.push(String.valueOf(this.infixExpression[i])); 
      } catch (Exception e) { 
       e.printStackTrace(); 
      } 
     } 
     else if(priority == 7){ 
      while(stack.top != 0){ 
       try { 
        lastData = stack.pop(); 
        if(!lastData.equals("(")){ 
         exp += lastData; 
        } 
        else{ 
         break; 
        } 
       } catch (Exception e) { 
        e.printStackTrace(); 
       } 
      } 
     } 
     else{ 
      try { 
       if(stack.top != 0){ 
        while(true){ 
         lastData = stack.pop(); 
         stack.push(lastData); 
         if(stack.top == 0 || lastData.equals("(") || priority(lastData.toCharArray()[0]) > priority){ 
          stack.push(String.valueOf(this.infixExpression[i])); 
          break; 
         } 
         exp += stack.pop(); 
        } 
       }else{ 
        stack.push(String.valueOf(this.infixExpression[i])); 
       } 

      } catch (Exception e) { 
       e.printStackTrace(); 
      } 
     } 
    } 
    if(stack.top != 0){ 
     try { 
      while(stack.top != 0){ 
       exp += stack.pop(); 
      } 
     } catch (Exception e) { 
      e.printStackTrace(); 
     } 
    } 
    return exp; 
} 
} 

但這並不與括號工作。

Answer 1

所有你需要的是：

1. 拆分輸入表達式項，分項乘數。
2. 添加緩衝部件和分隔符的順序，你需要

一些不好的代碼做到這一點：

public class Converter { 

    private String infix; 

    private void addMultPre(StringBuilder builder, String item) { 
     String[] multipliers = item.split("[*/]"); 
     for (int j = 0; j < multipliers.length - 1; j++) { 
      builder.append(infix.charAt(builder.length() + multipliers[j].length())); 
      builder.append(multipliers[j]); 
     } 
     builder.append(multipliers[multipliers.length - 1]); 
    } 

    private void addMultPost(StringBuilder builder, String item) { 
     String[] multipliers = item.split("[*/]"); 
     builder.append(multipliers[0]); 
     for (int j = 1; j < multipliers.length; j++) { 
      builder.append(multipliers[j]); 
      builder.append(infix.charAt(builder.length())); 
     } 
    } 

    public String prefix() { 
     String[] items = infix.split("[+-]"); 
     StringBuilder builder = new StringBuilder(); 
     for (int i = 0; i < items.length - 1; i++) { 
      builder.append(infix.charAt(builder.length() + items[i].length())); 
      addMultPre(builder, items[i]); 
     } 
     addMultPre(builder, items[items.length - 1]); 
     return builder.toString(); 
    } 

    public String postfix() { 
     String[] items = infix.split("[+-]"); 
     StringBuilder builder = new StringBuilder(); 
     char sign; 
     addMultPost(builder, items[0]); 
     for (int i = 1; i < items.length; i++) { 
      sign = infix.charAt(builder.length()); 
      addMultPost(builder, items[i]); 
      builder.append(sign); 
     } 
     return builder.toString(); 
    } 

    public Converter(String infix) { 
     this.infix = infix; 
    } 

    public static void main(String[] args) { 
     Converter c = new Converter("a+b*c"); 
     System.out.println(c.postfix()); 
     System.out.println(c.prefix()); 
    } 
} 

輸出：

abc*+ 
+a*bc