package String;

import java.util.List;

public class EncodeDecode {

public static void main(String[] args) {

List.of("aa", "aaabb", "", " qqqwwb bbbmmmm ")

.stream()

.map(String::trim)

.forEach(EncodeDecode::printEncodeDecode);

printEncodeDecode(null);

}

private static void printEncodeDecode(String str) {

System.out.println("original : " + str);

try {

String encodedString = encode(str);

String decodedString = (encodedString.equals(str)) ? str : decode(encodedString);

System.out.println("encoded : " + encodedString);

System.out.println("decoded : " + decodedString);

} catch (Exception e) {

System.out.println(e.getMessage());

}

}

private static String encode(String str) throws RuntimeException {

if (str == null || str.isEmpty())

throw new RuntimeException("no string to encode");

StringBuilder sb = new StringBuilder();

int counter = 1, n = str.length();

for (int i = 0; i < n; i++) {

char c = str.charAt(i);

while (i < n - 1 && c == str.charAt(i + 1)) {

counter++;

i++;

}

sb.append(c);

sb.append(counter);

counter = 1;

}

return sb.length() < n ? sb.toString() : str;

}

private static String decode(String str) throws RuntimeException {

if (str == null || str.isEmpty())

throw new RuntimeException("no string to decode");

StringBuilder sb = new StringBuilder();

int n = str.length();

for (int i = 0; i < n; i++) {

char c = str.charAt(i);

if (Character.isDigit(c) && i != 0) {

int counter = str.charAt(i) - '0';

while (counter > 0 && !Character.isDigit(str.charAt(i - 1))) {

sb.append(str.charAt(i - 1));

counter--;

}

}

}

return sb.length() == 0 ? str : sb.toString();

}

}