Julius Baer Singapore Interview Programming Challenge: How to write a Java Program for String Accumulator?

Introduction: Julius Baer Singapore have asked me to write this Java Program about String Accumulator. They gave around 1.5 Hours to complete the Program.

What is String Accumulator?

1. Create a simple string calculator with a method int add(String numbers).

  a. The method can take 0, 1 or 2 numbers and will return their sum (for an empty string it will return 0) for example “” or “1” or “1,2”.

  b. Start with the simplest test case of an empty string and move to 1 and 2 numbers.

2. Allow the add method to handle an unknown amount of numbers.

3. Allow the add method to handle new lines between numbers (instead of commas).

  a. The following input is ok: “1\n2,3” (will equal 6).

  b. The following input is NOT ok: “1,\n” (don’t need to prove it - just clarifying).

4. Support different delimiters.

  a. To change a delimiter, the beginning of the string will contain a separate line that looks like this: “//<delimiter>\n<numbers…>”, for example “//;\n1;2” should return 3 where the delimiter is ‘;’.

  b. The first line is optional, all existing scenarios should still be supported.

5. Calling add with a negative number will throw an exception with the message “negatives not allowed” - and the negative that was passed. If there are multiple negatives, show all of them in the exception message.

6. Numbers bigger than 1000 should be ignored, so adding 2 + 1001 = 2.

7. Delimiters can be of any length, for example: “//***\n1***2***3” should return 6.

8. Allow multiple delimiters like this: “//delim1|delim2\n” (with a “|” separating delimiters), for example “//*|%\n1*2%3” should return 6.

9. Make sure you can also handle multiple delimiters with length longer than one character.

Problem: How to write a Java Program to generate String Accumulator.

Solution: This Java Program will generate String Accumulator for provided String input.

Java Program:

package com.bo.bjb.service;

import org.apache.logging.log4j.LogManager;

import org.apache.logging.log4j.Logger;

import org.springframework.stereotype.Service;

import java.util.LinkedList;

import java.util.List;

@Service

public class StringAccumulatorService {

  private static final Logger LOGGER = LogManager.getLogger(StringAccumulatorService.class);

  public int add(String numbers) throws Exception {

    LOGGER.info("START ADD : numbers : " + numbers);

    int result = 0;

    if(numbers == null || numbers.trim().length() == 0){

       return result;

    }

    List<String> numberDataList = new LinkedList<>();

    if(numbers.contains("//")){

      int index = numbers.indexOf("\\n");

      LOGGER.info("START ADD : index : " + index);

      String delimeter = numbers.substring(2,index);

      LOGGER.info("START ADD : delimeter : " + delimeter);

      String data = numbers.substring(index+2);

      LOGGER.info("START ADD : data : " + data);

      String[] numberArrayAfterSplittingDelimeter = data.split("\\" + delimeter);

      for(String number: numberArrayAfterSplittingDelimeter){

        if(isNumber(number)){

          numberDataList.add(number);

        }else{

          if(number.contains("\n")){

            String[] numberArrayAfterSplittingNewLine = number.split("\n");

            for(String numberNewLine: numberArrayAfterSplittingNewLine){

              if(isNumber(numberNewLine)){

                numberDataList.add(numberNewLine);

              }

            }

          }

        }

      }

    }else{

      String[] numberArrayAfterSplittingComma = numbers.split(",");

      for(String number: numberArrayAfterSplittingComma){

        if(isNumber(number)){

          numberDataList.add(number);

        }else{

          if(number.contains("\n")){

            String[] numberArrayAfterSplittingNewLine = number.split("\n");

            for(String numberNewLine: numberArrayAfterSplittingNewLine){

              if(isNumber(numberNewLine)){

                numberDataList.add(numberNewLine);

              }

            }

          }

        }

      }

    }

    LOGGER.info("START ADD : numberDataList : " + numberDataList);

    List<String> errorNumbers = new LinkedList<>();

    for(String number: numberDataList){

      if(isNumber(number)){

        int numberValue = Integer.parseInt(number);

        if(numberValue <= 1000){

          if(numberValue < 0){

            errorNumbers.add(number);

          }

          result = result + numberValue;

        }

      }

    }

    LOGGER.info("START ADD : result : " + result);

    LOGGER.info("START ADD : errorNumbers : " + errorNumbers);

    if(!errorNumbers.isEmpty()){

      throw new Exception("Negatives not allowed. Negative Values : " + errorNumbers);

    }

    return result;

  }

  private boolean isNumber(String number){

    try {

      int data = Integer.parseInt(number);

      return true;

    }catch (NumberFormatException e){

      return false;

    }

  }

}

Java Unit Testing:

package com.bo.bjb.service;

import org.junit.jupiter.api.Assertions;

import org.junit.jupiter.api.BeforeEach;

import org.junit.jupiter.api.Test;

import static org.junit.jupiter.api.Assertions.assertEquals;

public class StringAccumulatorServiceTest {

  private StringAccumulatorService orderManagementService;

  @BeforeEach

  public void setup() {

    orderManagementService = new StringAccumulatorService();

  }

  @Test

  public void addTest() throws Exception {

    int result = orderManagementService.add("");

    assertEquals(0,result);

    result = orderManagementService.add("5");

    assertEquals(5,result);

    result = orderManagementService.add("5,7,8");

    assertEquals(20,result);

    result = orderManagementService.add("5,7,8,9");

    assertEquals(29,result);

    result = orderManagementService.add("5\n7,8,9");

    assertEquals(29,result);

  }

  @Test

  public void addTestNumberGreaterThan1000() throws Exception {

    int result = orderManagementService.add("5,7,10004");

    assertEquals(12,result);

    result = orderManagementService.add("10004");

    assertEquals(0,result);

  }

  @Test

  public void addTestNumberDelimiter() throws Exception {

    int result = orderManagementService.add("//;\\n1;2");

    assertEquals(3,result);

    result = orderManagementService.add("//***\\n1***2***3");

    assertEquals(3,result);

  }

  @Test

  public void addTestNegativeInput() {

    Exception exception = Assertions.assertThrows(Exception.class, () -> {

      orderManagementService.add("5,-7,-8");

    });

    Assertions.assertTrue(exception.getMessage().toLowerCase().contains("negatives not allowed"));

  }

}