压缩数组

public static String compressString(String S) {
    if(S == null || S.length() == 0){
        return S;
    }
    StringBuilder sb = new StringBuilder();
    char[] chars = S.toCharArray();
    int k = 0;
    sb.append(chars[k]);
    for (int i = 0; i <chars.length ; i++) {
        if(chars[k] != chars[i]){
            sb.append(i-k);
            k = i;
            sb.append(chars[k]);
            if(i == chars.length-1){
                sb.append(i-k+1);
            }
            continue;
        }
        if(i == chars.length-1){
            sb.append(i-k+1);
        }

    }
    return S.length()>sb.toString().length() ? sb.toString() : S;
}