StringCompression.java

/**
 * 443. String Compression
 * 
 * Given an array of characters chars, compress it using the following algorithm:
 * Begin with an empty string s.
 * For each group of consecutive repeating characters in chars:
 *  1. If the group's length is 1, append the character to s.
 *  2. Otherwise, append the character followed by the group's length.
 * The compressed string s should not be returned separately, but instead, be stored in the input character array chars.
 * Note that group lengths that are 10 or longer will be split into multiple characters in chars.
 * After you are done modifying the input array, return the new length of the array.
 * You must write an algorithm that uses only constant extra space.
 */

class StringCompression {
    public int compress(char[] theChars) {
        StringBuilder s = new StringBuilder();
        s.append(theChars[0]);
        int counter = 1;
        if (theChars.length > 1) {
            for (int i = 1; i < theChars.length; i++) {
                //1-letter case
                if (theChars[i] == theChars[i - 1]) {
                    if (i == theChars.length - 1)
                        s.append(++counter);
                    else
                        counter++;
                } else {
                    if (counter > 1) {
                        s.append(counter);
                        s.append(theChars[i]);
                    } else
                        s.append(theChars[i]);
                    counter = 1;
                }
            }
            for (int i = 0; i < s.length(); i++)
                theChars[i] = s.charAt(i);
        }
        return s.length();
    }
}