给定一个字符串 (100*((2+12)/5))/14，如何在每个运算符和数字之间添加空格？

Question

For example I want to go from this string

(100*((2+12)/5))/14

to this

( 100 * ( ( 2 + 12 ) / 5 ) ) / 14

Answer 1

You can do it as

"(100*((2+12)/5))/14".replaceAll("\\D", "$0 ").replaceAll("\\d+", "$0 ").trim();

Explanation:

1. \D specifies a non-digit character which will be replaced with the character plus space.
2. After the above replacement is done the second replacement will be applied on the returned string. In that replacement, \d+ specifies an integer number which will be replaced with the number plus space.
3. Finally, the trailing and leading space will be removed by trim() .

Demo

public class Main {
    public static void main(String[] args) {
        String expression = "(100*((2+12)/5))/14";
        expression = expression.replaceAll("\\D", "$0 ").replaceAll("\\d+", "$0 ").trim();

        System.out.println(expression);
    }
}

Output:

( 100 * ( ( 2 + 12 ) / 5 ) ) / 14

Answer 2

You can iterate over all characters, and then check if:

• if it's the last character don't do anything
• if the current index character is not a digit then add a space after it
• if the current index character is a digit but the next character isn't then add a space after it

public static void main(String[] args)
    {
        String str = "(100*((2+12)/5))/14";
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < str.length(); i++)
        {
            char c = str.charAt(i);
            sb.append(c);
            if (i < str.length() - 1)
            {
                if ((Character.isDigit(c) && !Character.isDigit(str.charAt(i + 1))) || !Character.isDigit(c))
                {
                    sb.append(" ");
                }
            }
        }

        System.out.println(sb.toString());
    }