American Express Engineer 1 Interview Questions and Answers

Round: Test
Experience: The test was on hackerrank.
Tips: * Fast coding and problem solving required
* Time crunch
* The test is valued a LOT in the hiring process
Duration: 120 minutes
Total Questions: 4

Round: Technical Interview
Experience: Question 1 : He tried to take the discussion to web based technologies to which I straightly told I don’t know. Not sure if that was a good decision. Nevertheless, he went over my resume a lot of times and asked about various projects.
Question 2 : Discussed the various projects related to it.
Question 3 : He asked this question because I had worked on django during my FB internship. I proposed a tree based structure. xyz.com/a/b/c ---> b is child of a, c is child of b.

Question 4 : Next he moved to a very interesting question. Given a simple text editor, I want to facilitate autocomplete feature. We discussed about syntactic methods using language specific keywords. I suggested a trie based implementation which he liked. Later he asked me to improve and redirected me to using scope of the variables, and grammar of the language. We discussed about all the steps I did in language translators lab (macrojava -> minijava -> typechecking -> miniIR -> microIR -> miniRA ->Mips) where we built a Java compiler in Java. We later hopped back to original question and I suggested that we can use grammar to to store multiple (nested kind of) tries for different scope. He asked me how would I define “scope”. He gave me a scenario which helped me come up with the nested trie structure
int a;
{
int b;
{
int c; //a b c can be used
}
{
int d; //a b d can be used
}
}
He then asked me details of how I would code. I said we could use the respective visitors and maintain the current trie root for scope. He liked it but I missed at 2 places :
1. He asked me about token generation used in a compiler and I said flex and bison. I was expected to elaborate a bit.
2. He asked me how the grammar is generated and how the visitors are invoked. I couldn’t explain properly because I was not thorough with it.
Tips: * Keep smiling in the interviews.
* My interviewer had hopped from Microsoft to Visa. We had a short detailed discussion on how the transition was and what drove him to do that.
* It’s always good to know about the company to pick up interesting discussions, read up latest articles and news
* The interviewers want to see if you are passionate about what they are building. Their PPT (Pre Placement Talk) was also focussed majorly on the technologies they are building.
* If you take a question in a direction, make sure you are very very thorough with it. I took it in the direction of compilers, but couldn't make the transition seamlessly because I wasn't thorough with a lot of things (like token generation, visitor invocation).
* Not sure if telling upfront that you don't know about web technologies when you are applying for a profile that might need it is a good idea or not.


Round: Technical Interview
Experience: I think he was a senior person and spoke very passionately about the work that is happening in visa Bangalore office.

Question 1 : I said maybe I should have learnt a little about web based technologies. I think he was looking for a more generic answer.
Question 2 : I went ahead with calculating the expected score where my score random variable = 1 with probability p, and 0 with probability (1-p). I conditioned that expected score of game1 > game2 which would give me the range of p. I goofed up the equations twice but he said he liked my approach and I was just there

Question 3 : I suggested building a graph where a node is a word and an edge means a transition, and then performing BFS. He said that was obvious and that he was more interested in knowing how I build the graph. I suggested a method to reduce the number of string comparisons by storing a count vector with each word. Count vector is a 26 length vector where count[i] = number of times that letter occurs in the word. I would do string comparison to identify neighbours only if the difference in count vectors in 2. Eg, cot = cat - a + o. String comparison is still needed because of false positives. Eg, oct = cat - a + o but cat -> oct is not a valid transition. He liked my approach and asked me to code, discussed the complexity.
Tips: * Don't be naive around a senior engineer. Be confident.
* Explain your approach before going ahead solving it. I missed that in Q1 and for a long time he didn't know what I was heading towards.
* Write clean code, practice coding on paper to make sure you write compilable code. Shabby code is a turn off.
* Show passion for the company you are applying for.

General Tips: * Be friendly and keep smiling.
* Know about the company, well in detail. Recent news, articles, acquisitions, organisational changes, new offices, new product, etc.
* Know about the volume the company handles, certain mind boggling figures, what the company *does not* do
* If you are introducing yourself as an expert in a certain field, be prepared for questions like "How will you contribute to our company with your expertise" type of questions.
* Be very very thorough with every single thing you write on your resume. A small point you weren't sure about might become the basis of your whole interview. Don't write things you are unsure of, or have worked very little on.
Skill Tips: * I think I didn’t take Visa very seriously. I was assuming they won’t take a undergrad and they won’t take me because I have 0 knowledge in web based technologies. I might have acted a little cocky.
* They had nice pie diagrams which shows that they had done thorough research about each and every candidate based on resume and the coding test.
* They value the coding test a lot.
* Be very thorough with the projects you write on resume. They will give you a problem which won't be straightforward and will map onto one of your course projects. You are expected to do the mapping seamlessly. Every bit of the discussion you have with the interviewer can be your next problem.
* Brush up on web based technologies if you can.
* There will be a HR round as well if you clear the technical interviews.

Skills: Maths(esp Probability), Design, Passion, Web Technologies, Technical Skill And Speaking Skill, Coding Skills
College Name: IIT Madras
Motivation: * Been the leader since more than half a century, been through the technological revolution.
* Revolutionising payments architecture. Building something of greatest need, so elegant and optimised, yet producing such consistent performance.
* Keeping up with the need of the generation by introducing features which are brand new. Eg, “all-purpose credit card”.
* Loved their PPT (Pre Placement Talk). Volume of the data and processing is IMMENSE. Billions of transactions in a year voluming up to trillions. More than 200 countries in the world --> these stats are HUGE.
* Fraud detection is a space I would have loved to work on given that I come from a Data Mining background.

Funny Moments: Chucked out before HR round :P