public class Solution {

  public String decompress(String input) {

    // Write your solution here

    if (input.length() == 0) {

      return input;

    }

    StringBuilder sb = new StringBuilder();

    int i = 0;

    char[] charArr = input.toCharArray();

    char prevChar = input.charAt(0);

    while (i < charArr.length) {

      char cur = charArr[i];

      if (Character.isLetter(cur)) {

        prevChar = cur;

        i += 1;

      } else if (Character.isDigit(cur)) {

        int num = cur - '0';

        if (num == 0) {

          i += 1;

        } else {

          while (i + 1 < charArr.length && Character.isDigit(charArr[i + 1])) {

            num = 10 * num + (charArr[i + 1] - '0');

            i += 1;

          }

          for (int j = 0; j < num; j++) {

            sb.append(prevChar);

          }

          i += 1;

        }

      }

    }

    return sb.toString();

  }

}

public class Solution {

  public String decompress(String input) {

    // Write your solution here

    char[] charArr = input.toCharArray();

    StringBuilder sb = new StringBuilder();

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

      char cur = charArr[i++];

      int num = charArr[i] - '0';

      for (int j = 0; j < num; j++) {

        sb.append(cur);

      }

    }

    return sb.toString();

  }

}