Randomise each element of String from inside? Java-CodePudding

Hello I am trying to change the place of characters in a string. But the first and last have to stay like they are. For example:

String str = "String test print out";

The output should be for example:

Sirntg tset pirnt out

The first and last charakter of each word have to stay the rest have to change randomly: Here is the code I already did, I tryed to splitt the element of the string in an array and splitt them but its not working:

import java.util.*;
public class Main
{
    public static void main(String[] args) {
        String str = "String test out";
        String[] words = str.split("\\s");
        Random rnd = new Random();
        ArrayList<Integer> digitList = new ArrayList<Integer>();
       
       for(int j = 0;0<=words[].length();j  ){
            int lst = words[j].length();
            char first = words[j].charAt(0);
            char last = words[j].charAt(words[j].length() - 1);
            
            for(int i =1, random = 0; i < words[j].length()-1; i  ){
                do{
                    random = rnd.nextInt(words[j].length()-2) 1;
                }while(digitList.contains(random));
            
                digitList.add(random);
                System.out.print(words[j].charAt(random));
            }
        
        }       

    }
}

CodePudding user response：

You could make use of some nifty functionality in Java's collection framework:

public static void main(String[] args) {
    String str = "String test out";

    for (String word : str.split("\\s")) {
        List<Character> chars = word.chars()
                .mapToObj(e -> (char) e)
                .collect(Collectors.toList());

        // shuffle the letters in the word, except for the first one and last one
        Collections.shuffle(chars.subList(1, chars.size() - 1));

        String shuffledWord = chars.stream()
                .map(String::valueOf)
                .collect(Collectors.joining());

        System.out.println(shuffledWord);
    }

}

CodePudding user response：

Here is a really efficient way to do it. Instead of splitting, changing strings and merging them back together, create a single StringBuilder and use a Pattern to go through each word, scramble them and then return the string.

/** This pattern matches a word, and group 1 excludes the first and last letter. */
static final Pattern WORD = Pattern.compile("\\b\\w(\\w{2,})\\w\\b");

public String scrambleWords(String input) {
    Random random = new Random();
    StringBuilder s = new StringBuilder(input);
    Matcher m = WORD.matcher(input);
    
    while (m.find()) {
        int start = m.start(1);
        int end = m.end(1);
        for (int i = start; i   1 < end; i  ) {
            int j = random.nextInt(i   1, end);
            char c1 = s.charAt(i);
            char c2 = s.charAt(j);
            s.setCharAt(i, c2);
            s.setCharAt(j, c1);
        }
    }
    
    return s.toString();
}