Printing a 3-in-3 formatted sequence of numbers separated by dash

Question

Let’s say I have the following entry String S = "00-44 48 5555 8361" and that I need to return this character string divided 3 by 3, separated by "-", as follows:

Output: 004-448-555-583-61

The amount of characters may vary. Below the following scope:

public class Solution{
    public static String solution(String S){
    }
}

public static void main(String[] args) {    
        String S = "00-44  48 5555 8361";   
        System.out.print(solution(S));

    }

}

In an effective way, how to solve this in Java 8?

Answer 1

Regex does magic:

class Solution {
    public static void main(String[] args) {
        String s = "00-44  48 5555 8361";
        System.out.println(solution(s));
        String s2 = "00-44  48 5555 8361 xxx 1";
        System.out.println(solution(s2));
        String s3 = "12345";
        System.out.println(solution(s3));
    }

    public static String solution(String s) {
        return s.replaceAll("[^\\d]", "").replaceAll("...", "$0-").replaceAll("-$", "");
    }
}

Here’s the way out:

004-448-555-583-61
004-448-555-583-611
123-45

See here working on ideone.

Explanation:

• The replaceAll is a method that operates on three strings: The instance over which the method is called (A), the first parameter (B) and the second parameter (C). This method searches for occurrences of the regular expression of B within the string A and replaces them with C, returning the result after all substitutions have been made. References denoted with $ can be used in C to reference groups defined in B.

• The replaceAll("[^\\d]", "") uses regular expression [^\\d]. This regular expression is meant to represent anything other than a number. The excerpt \\d is what represents a number. The [^ ... ] indicates all characters except those between the [^ and the ]. Soon, [^\\d] represents all characters except numerical ones. Thus, this will replace any character other than a number with the empty string. That is, it serves to boot all non-numeric characters from the string.

• The replaceAll("...", "$0-") uses regular expression .... The . represents any character, therefore ... are three characters. As the previous regular expression has already eliminated non-numeric ones, so this hence finds the digits in groups of three on three. Therefore, this expression replaces each trio of numerical characters by what is represented by $0-. It turns out that $0 represents everything the regular expression found, which in this case is the three characters found. Therefore, this will replace each three characters by these same characters followed by a -.

• It may be that about a - in the end, as in the case of "00-44 48 5555 8361 xxx 1". That’s why we have the replaceAll("-$", ""). The regular expression -$ means a - followed by the end of the string (which is represented by $). This means that the dash at the end of the string (if any) will be replaced by an empty string. That is, deleted.