American Express Interview Questions, Process, and Tips for Freshers

There was 25 MCQ-type question.

There was 3 coding question based on DSA.

Basic questions also with coding test

Coding questions asked in this round

Q1. Oops concept amd design patterns asked
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Q2. Explain Singleton design pattern.
Ans. 
Singleton design pattern restricts the instantiation of a class to one object.
• Ensures only one instance of a class exists in the system

• Provides a global point of access to that instance

• Used when only one instance of a class is required throughout the system

• Example: Database connection manager, Logger class
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Q3. Explain oop concepts class, encapsulation etc
Ans. 
OOP concepts include class, encapsulation, inheritance, and polymorphism.
• Class is a blueprint for creating objects with shared properties and methods.

• Encapsulation is the practice of hiding implementation details and exposing only necessary information.

• Inheritance allows a class to inherit properties and methods from a parent class.

• Polymorphism allows objects to take on multiple forms or behaviors depending on the cont...read more
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Round duration - 120 minutes
Round difficulty - Easy

It consisted of 3 coding questions which were purely based on Data Structures and Algorithms.

Question 1 - Find the length of the longest switching sub-array. An array is called switching if all numbers in even positions are equal and all numbers in odd positions are equal. 


Question 2 - It was a long passage question on Dynamic Programming but the solution was really easy.

Question 3 - Given a string S consisting of N lowercase letters, return the minimum number of letters that must be deleted to obtain a word in which every letter occurs a unique number of times. Ex - "aaaabbbb" should return 1, as when we delete 1 a or 1 b , a and b will have different frequencies.


The major point to note in the coding round was that they did not have any time or space limit, so brute force solutions were also accepted. 
The result of my test was declared just as the test ended and I scored a 100%, but they took a long time to release the final shortlist. There was a gap of about a week between the test and interviews.

Q1. 
Longest Switching Subarray Problem Statement
Determine the length of the longest contiguous subarray in a given array of positive integers, where the subarray qualifies as 'switching'. An array is defined...read more
Ans. 
It's like a sliding window problem.
We keep track of even and odd equality with 2 variables, even and odd.
Whenever we come across a unmet condition, like index even but not equal with even variable and same goes for odd, we first
Record the length till now in max_len.
Reset start to i-1 as this is need incase of all elements equal.
Reset even and odd according to current index i to arr[i] and arr[i-1] respectively.
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Q2. 
Unique Frequency Problem Statement
Given a string 'STR' with lowercase letters, determine the minimum number of deletions required to ensure that every letter in the string appears a unique number of time...read more
Ans. Brute Force
As we are only allowed to delete the character, thus the resulting string after deletion of some character would be the subsequence of the string. So, we have to find such a subsequence which has the unique frequency of each character. 
 
Initialise a variable ‘ans’ that will store the minimum number of characters that are needed to remove from the string. Create all the subsequences of the string an...read more
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Round duration - 40 minutes
Round difficulty - Easy

Amex came for two profiles - Tech Role and Analyst, 19 and 23 people respectively were shortlisted for the interviews. Fortunately, I was shortlisted for both the roles. I was asked basic question of C++ and it was majorly an HR Round

Round duration - 20 minutes
Round difficulty - Easy

It was a fairly simple round conssting of 5 - 6 questions related to coding, puzzles and me.

What are your interests? 
What projects have you done and your field of interest?

Round duration - 50 minutes
Round difficulty - Easy

This round was purely technical
No introduction was done, straight to the point

My preference was the Tech Role, so as I was selected in this, I never had to give interviews for the Analyst role. In total 5 people were selected in the Analyst profile and 4 in the Tech profile.

In the end, I was offered a 6 months internship at Amex.

Q1. 
Palindrome Linked List Detection
Given a singly linked list of integers, determine if it is a palindrome. A linked list is considered a palindrome if it reads the same forward and backward.
Example:
Inp...read more
Ans. 
I gave the two pointer approach. Then he said what if we are provided with the length of the list. I said that we will move forward in the list till n/2 nodes and then the same approach as above. Then he said what if we had to do it with a stack. I said we will add elements into the stack till n/2 nodes and then start popping elements while simultaneously traversing the linked list from the (n/2+1)th node till n if the...read more
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Round duration - 120 minutes
Round difficulty - Easy

The coding round was at 11 am in the morning. The questions were of medium level. The questions were purely based on Data Structures and Algorithms.

Q1. 
Sliding Maximum Problem Statement
Given an array of integers ARR of length 'N' and a positive integer 'K', find the maximum elements for each contiguous subarray of size K.
Example:
Input:
ARR = [3, 4,...read more
Ans. Brute Force
1. We know that an array of size ‘N’ will have in total ‘N’ - ‘K’ - 1 subarray of size ‘K'.
2. Thus, what a trivial solution suggests is that we traverse over all subarrays of size ‘K', and calculate the maximum element in each of these subarrays individually.
3. So, we can run two nested loops, the outer one will iterate over the starting index of the subarray, and the inner loop will be used to calculate the max...read more
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Q2. 
Longest Substring with At Most K Distinct Characters
Given a string S of length N and an integer K, find the length of the longest substring that contains at most K distinct characters.
Input:
The first...read more
Ans. Brute Force
• We will generate all the substrings using 2 nested for loops and we will have a ‘CHECK’ function which returns true if the number of distinct character in the substring is less than equal to K otherwise false.
• We will have an ans variable initialize to 0. We will call the ‘CHECK’ function with every substring and if it returns true then
  • ANS = MAX(ANS , CURRENT_SUBSTRING.SIZE())
• To implement the check function w...read more
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Round duration - 45 minutes
Round difficulty - Easy

I was selected for the interview. The interview was conducted early in the morning at 10 am. The interviewer was very friendly and calm.

Round duration - 30 minutes
Round difficulty - Easy

This round was a mix of technical, puzzles and HR. The interview was fairly easy, The interviewer asked for my introduction and continued with the interview then.

Q1. 
Stack using Two Queues Problem Statement
Develop a Stack Data Structure to store integer values using two Queues internally.
Your stack implementation should provide these public functions:
Explanation:
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Ans. Approach 1
• This method ensures that every new element entered in the queue ‘q1’ is always at the front.
• Hence, during pop operation, we just dequeue from ‘q1’.
• For this, we need another queue ‘q2., which is used to keep every new element to the front of ‘q1’.
• During push operation :
  • Enqueue new element ‘x’ to queue ‘q2’.
  • One by one, dequeue everything from ‘q1’ and enqueue to ‘q2’.
  • Swap the names of ‘q1’ and ‘q2’.
• During pop o...read more
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Round duration - 45 minutes
Round difficulty - Easy

This was the last round for getting selected as an intern. However, this was a pure technical round. Only coding questions were asked. Also, at the end he asked me the question, Why American express?

Q1. 
Detect and Remove Loop in Linked List
For a given singly linked list, identify if a loop exists and remove it, adjusting the linked list in place. Return the modified linked list.
Expected Complexity:
A...read more
Ans. 
1. Traverse linked list using two pointers, that is, slow and fast pointer
2. Move slow pointer by one and fast pointerby two.
3. If these pointers meet at the same node then there is a loop. If pointers do not meet then linked list doesn’t have a loop.
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Q2. 
Interval List Intersection Problem
You are provided with two sorted lists of closed intervals, INTERVAL1 and INTERVAL2. A closed interval [x, y] (x < y) signifies the set of real numbers z such that x ...read more
Ans. Two-Pointer Approach
The main intuition behind this approach is that ‘INTERVAL1’ and ‘INTERVAL2’ are already sorted. So two cases arise:
 
1. If INTERVAL1[0] has the smallest endpoint, it can only intersect INTERVAL2[0]. After that, we can discard INTERVAL1[0] since it cannot intersect with anything else.
2. If INTERVAL2[0] has the smallest endpoint, it can only intersect INTERVAL1[0]. After that can discard INTERVAL2[0] si...read more
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