我编写的代码将postfix转换为完全括号的中缀,作为我作业的一部分,但是这段代码只能将中缀表达式转换为单位数字。我需要帮助转换中缀表达式的数字为2位或更多位数。
//Here's my code. My class doesn't use collection in JAVA.
//Classes and Interfaces for stack, list, and tree are provided.
private static final String DIGITS = "0123456789";
public static String convertPostfixtoInfix(String toPostfix)
{
LinkedStack<String> s = new LinkedStack<>();
for(int i=0; i<toPostfix.length(); i++)
{
if(DIGITS.indexOf(toPostfix.charAt(i)) != -1)
{
s.push(toPostfix.charAt(i)+"");
}
else if(toPostfix.charAt(i) == " ");{}//do nothing for blank.
else
{
String temp = "";
temp += toPostfix.charAt(i);
String num1 = s.top();
s.pop();
String num2 = s.top();
s.pop();
s.push("(" + num2 + temp + num1 + ")");
}
}
return s.top();//top() is same as peek() method.
}
例如,使用此代码,
输入:4 5 - 9 2 1 + / *
输出:((4-5)*(9 /(2 + 1)))
输入:40 5 - 9 20 1 + / *
输出:(9 *(2 /(0 + 1)))
这是你如何做到的。
首先,一点点通知。这行代码是多余的:
private static final String DIGITS = "0123456789";
如果你想检查一个字符是否是数字,你可以简单地用它来做
Character.isDigit();
但为了简单起见,我将这条线留下了。
现在,回到你的代码。为了提供解析多个数字的功能,您需要做的就是在遇到数字时循环输入String,直到第一个非数字字符。
我已经更改了一些代码,以向您展示它应该如何工作的基本概念:
private static final String DIGITS = "0123456789";
public static String convertPostfixtoInfix(String toPostfix)
{
LinkedStack<String> s = new LinkedStack<>();
StringBuilder digitBuffer = new StringBuilder();
/* I've changed the 'for' to 'while' loop,
because we have to increment i variable inside the loop,
which is considered as a bad practice if done inside 'for' loop
*/
int i = 0;
while(i < toPostfix.length())
{
if(DIGITS.indexOf(toPostfix.charAt(i)) != -1)
{
//when a digit is encountered, just loop through toPostfix while the first non-digit char is encountered ...
while (DIGITS.indexOf(toPostfix.charAt(i)) != -1) {
digitBuffer.append(toPostfix.charAt(i++)); //... and add it to the digitBuffer
}
s.push(digitBuffer.toString());
digitBuffer.setLength(0); //erase the buffer
}
//this if-else can also be replace with only one "if (toPostfix.charAt(i) != ' ')"
else if(toPostfix.charAt(i) == ' ');{}//do nothing for blank.
else
{
String temp = "";
temp += toPostfix.charAt(i);
String num1 = s.top();
s.pop();
String num2 = s.top();
s.pop();
s.push("(" + num2 + temp + num1 + ")");
}
i++;
}
return s.top();//top() is same as peek() method.
}
输入:40 5 - 9 20 1 + / * 输出:((40-5)*(9 /(20 + 1)))