8 String Interview Questions and Sample Answers

By Indeed Editorial Team

Updated 7 December 2022

Published 7 May 2022

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

In programming, strings are a data type that holds information. You can use them to store sequences of characters or text in a computer program. Understanding the types of questions that can occur during an interview for a programming position can help you better answer them. In this article, we review how you can address a string programming interview question, provide sample questions with answers and list tips you can use for your interview.

Answering a string programming interview question

You can use the following approaches to address a string interview question:

  1. Understand the question. Before attempting to answer a question, ensure that you know what the question requires. This step can allow you to think of a suitable solution.

  2. Consider different string operations. You can think about what kinds of string operations apply to the question. For example, if the question is about finding a substring in a string, you might consider different string search algorithms.

  3. Try to create a simple solution. You can start by developing a solution that works for one string example. Having a simple working solution for one question can motivate you to solve the others.

  4. Improve the simple solution. If your solution works well on one example, you can create other models and test how the solution performs. For instance, if your method can search for a character in a lowercase string, you could enhance it to search in uppercase strings.

  5. Explain your solution. Describe each step of your answer to the interviewer. Doing so can help them understand your thought process.

Related: Stepped Guide on How to Ace an Interview: Tips and Examples

8 string programming interview questions with sample answers

Here are eight examples of string questions you might encounter during a programming interview:

1. How do you identify the most frequent character in a string?

The interviewer may ask this question to test your ability to count the occurrence of characters in a string. They may ask you to examine a string that has duplicate characters. You can take this opportunity to explain how you might go about identifying the most duplicated letter.

Example: 'To identify the most frequent character, you can use a 'for loop' to iterate through the string. You can store the number of times each character appears in a variable for each iteration. The character with the largest number of appearances is the most frequent.'

Related: How to Write Pseudocode (With Advantages and Disadvantages)

2. How do you reverse a string?

When writing a program, some applications may require your knowledge of how to reverse characters in a string. For example, if you build a tool that analyses text, you might decide to invert the text variable. Then, you can quickly analyse it from the end to the beginning. The interviewer may be testing your ability to use reversed strings. You can explain by listing the steps to follow when flipping strings.

Example: 'Depending on the programming language, there are different ways to reverse a string. Some languages, such as Java, have a 'reverse' function that you can use on a string. You can also convert the string to an array and reverse the array. Finally, you convert the reversed array back to a string.'

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3. Are strings thread-safe?

You can describe a thread as a flow of instructions within a piece of code. Threads allow programmers to create sections in the code that appear to run simultaneously. The hiring manager may ask this question to test your experience with using strings in threaded code. You can describe your understanding of thread safety and whether string variables satisfy that safety requirement.

Example: 'If a data type is thread-safe, it means different threads can concurrently read and change its data in the correct order. Typically, strings are unsafe for threads. This is because programs often store strings in shared memory. Multiple threads may try to access or change the string data simultaneously. This concurrent access can lead to corruption of the data you've stored in the string.'

4. Can you convert strings to integers?

In some computer programs, strings can be easier to manipulate than integers. Therefore, you may store the data in a string type and convert it to an integer. The employer can ask this question to identify how familiar you are with converting strings to other data types. You can answer this question by explaining when converting strings to integers is possible and when it might fail.

Example: 'You can convert a string to an integer if it contains numerical characters. If a string contains non-numerical characters, the integer conversion may cause an error. For example, converting the string 'hello' to an integer fails.'

Related: 4 Types of Data (With Examples, Differences and Techniques)

5. Are strings suitable for storing passwords?

The hiring manager may use this question to test your familiarity with creating secure applications. Since passwords identify a user's account, insecure storage of passwords can expose users' accounts to attackers. You can answer by explaining what makes strings suitable for password storage.

Example: 'The primitive strings, which we identify as 'char', are suitable for passwords while 'String' objects in Java are insecure. 'Chars' are mutable. This mutability means you can clear the elements of a 'char'. This feature can mitigate the risk of an attacker stealing the password. 'String' objects are immutable. Thus, their content is unchangeable. The immutability poses a threat because the contents of a 'String' remain in a program's memory for a long duration. When this happens, a malicious program may have a higher chance of reading the passwords.'

Related: What Does a Computer Programmer Do? (With Career Steps)

6. How do you remove duplicates from a string?

Duplicate strings in data can occupy a lot of storage space. They can also cause errors when programs try to analyse or process the data. The interviewer can ask this question to test your experience in keeping string data organised and free of erroneous duplications. You can answer by explaining the process you follow when removing string duplicates.

Example: 'To remove string duplicates, you can use a set, a loop or a map. A set is a data structure that only allows unique values. By converting the string into a set, you discard duplicate letters. A loop involves iterating through the characters and adding each to a new string variable. You then keep track of which characters are missing in the new variable. If a character is already in the new string, you skip it.

A map creates key-value pairs of the data. In this problem, the keys are the characters in the string, while the values are their frequency. You then add the characters with a frequency count of one to a new string.'

Related: 6 Types of Java Certification (Plus Tips to Achieve Them)

7. What encoding do strings use?

Computer programs may represent data using distinct character encoding. If you encode a string using a different character set from the one in your system, the string contents may display incorrectly. The hiring manager may ask this question to test your understanding of the importance of using the proper encoding of data. You may answer by showing the encoding that string types utilise.

Example: 'The character encoding in strings is Unicode. It's a standard that defines a set of characters that applications can use in written communication. The most common character encodings are UTF-8 and UTF-16. Some systems may also use ASCII to represent the characters of the alphabets, some symbols and digits. Unicode can represent information in multiple languages, including Greek and Arabic. This support for varied languages is missing in the ASCII representation.'

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8. How can you identify if a string is a palindrome?

A palindrome string is one you can spell the same way backwards as the original string. For example, 'Anna' has the exact spelling when you reverse the letters. An interviewer may use this question to examine your ability to identify patterns in a string problem and develop a solution based on the pattern. Your response can include the different approaches you might use to identify a palindrome.

Example: 'There are various ways to identify if a string is a palindrome. One approach is to reverse the string and compare it to the original string. If they're the same, then the string is a palindrome. Another solution is to iterate through the string and compare the first character to the last character, then the second character to the second last. You repeat this process until you arrive at the middle of the string. If all the letter comparisons match, the string is a palindrome.'

Related: What Does It Take to Be a Software Engineer?

Tips to help you prepare for a string interview

Here are a few tips that can help you prepare for your string programming interview:

  • Review your knowledge about strings. Ensure you understand the fundamental string operations, such as iterating through a string or reversing a string. You can approach most string questions with this basic knowledge.

  • Research the company. String problems can have different solutions depending on the programming language. Researching the company can tell you about the questions they're likely to ask based on their coding language.

  • Practise answering interview questions. You can request a friend familiar with programming to help you familiarise yourself with questions. They can ask you questions and provide guidance when you require it.

Related: 10 Tips for What to Do Before an Interview (With Importance)

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