How to count characters in order in a String?

Question

I have a String for an editor in a 2D platform game, where the user clicks on a 16x60 rectangle board to create a custom board. I loop through these rectangles and get a String that I'd like to trim down. The x's are blocks, and a's are empty space. I need this to draw the level.

String s = "x1x1x1x1a1a1x1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1";

I want to trim this to x4a2x1a54. Basically adding up the x's and a's that show up right after each other.

How do I do this?

Answer 1

Loop though the characters and store the last alphabetic character. For each of those chars parse the number that follows it. It the alphabetic char is the same as the last one you can add this number to the count, otherwise write the old results to the output:

public static String compress(String input) {
    if (input == null || input.isEmpty()) {
        return input;
    }
    char type = ' ';
    int count = 0;
    StringBuilder output = new StringBuilder();
    int index = 0;
    final int length = input.length();
    while (index < length) {
        char elementType = input.charAt(index);

        // parse number
        int elementCount = 0;
        char c;
        for (index++; index < length && Character.isDigit(c = input.charAt(index)); index++) {
            elementCount = 10 * elementCount + (c - '0');
        }

        if (elementType == type) {
            count += elementCount;
        } else {
            // finish counting last type
            output.append(type).append(count);
            type = elementType;
            count = elementCount;
        }
    }
    output.delete(0, 2); // remove substring added for the initial count/type
    output.append(type).append(count); // append last entry
    return output.toString();
}

This allows you to output numbers different to 1, e.g.

compress("a22a20x9")

Answer 2

Just to let you know, stackoverflow is not a forum to get code but to help you with your code and point out errors or give suggestions.

I rather dislike a demand but since this problem catched me a bit here is my version of it. Unfortunatelly I wasn't able to use only Streams and had to add an Arraylist to it (maybe with the reduce and collect methode of streams it is possible in one line) but it works as intended.

    String s = "x1x1x1x1a1a1x1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1";
    ArrayList<String[]> map = new ArrayList<>();
    for(String c:s.split("(?<=\\G..)")){
        if(map.isEmpty()||!map.get(map.size()-1)[0].equals(c.substring(0,1))){
            map.add(new String[]{c.substring(0,1),c.substring(1)});
        } else{
            map.get(map.size()-1)[1]=(Integer.parseInt(map.get(map.size()-1)[1])+Integer.parseInt(c.substring(1)))+"";
        }
    }
    StringBuilder sb = new StringBuilder();
    map.forEach(x-> sb.append(x[0]).append(x[1]));
    System.out.println(sb.toString());

EDIT: I changed the code so that other numbers than 1 are also added to the String and I did not use Streams for now on but for-loops

Answer 3

The first thing that I would suggest is breaking this string down into easier to manage sections like this:

    String s = "x1x1x1x1a1a1x1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1a1";
    String[] splitS = s.split("1");
    //Contents of the array are: [x, x, x, x, a, a, x, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a]
    //We can now loop through each string in the string array and count how many we have of what
    ArrayList<String> values = new ArrayList<String>();
    int start = 0, end = 0, grandCounter = 0;
    String current = splitS[0];
    for(int i = 1; i < splitS.length-1; i++){
        if(!splitS[i].equals("x") && current.equals("x")){
            end = i;
            values.add("x" + (end - start));
            grandCounter += (end-start);
            start = end;
            end = 0;
            current = "a";
        } else if(!splitS[i].equals("a") && current.equals("a")){
            end = i;
            values.add("a" + (end - start));
            start = end;
            end = 0;
            current = "x";
            grandCounter += (end-start);
        }
    }
    values.add( "a" + (splitS.length-grandCounter) + "");
    System.out.println(values.toString().replace("[", "").replace(",", "").replace("]", "").replace(" ", ""));

The above code exactly returned the following when told to print in console: x4a2x1a58

Please let me know if you have any further questions or issues with your work!

Answer 4

Here's a simpler method than the ones already posted:

 public static String customTrim(String s){

String res = "";
String last = "";
int count = 0;

for (int i = 0; i < s.length() - 1; i+=2){

  String curr = "" + s.charAt(i) + s.charAt(i+1);

  if(!curr.equals(last)){
      count = 1;
      res += "" + s.charAt(i) + count;
  }

  else{
    int subLength = ("" + count).length();
    count++;
    res = res.substring(0, res.length()- subLength) + count;
  }

  last = curr;

}
return res;
}

Answer 5

You could do it the way fabian posted, which works just fine. However, I figured it out myself by just having three simple if's.

    StringBuilder sb = new StringBuilder();

    List<String> values = new ArrayList<>();

    String s = "x1x1x1x1a1a1x1x1a1a1a1";
    String[] splitString = s.split("1");
    // "xxxxaaxxaaa"
    // to x4a2x2a3

    String current = splitString[0];
    int occ = 0;

    for(int i = 0; i < splitString.length;i++){

        if(!splitString[i].equals(current)){
            values.add(current+occ);
            occ = 0;
            current = splitString[i];
        }

        if(splitString[i].equals(current)){
            occ++;
        }

        if(i == splitString.length-1){
            values.add(current+occ);
        }

    }

    for (String str: values
         ) {
        sb.append(str);
    }

    System.out.println(sb);
}