American Express Technical Support Engineer Interview Questions and Answers

Round duration - 90 minutes
Round difficulty - Medium

This was an online test for 90 minutes. 2 programming questions and MCQs related to CS fundamentals were asked.

Q1. 
Cycle Detection in a Singly Linked List
Determine if a given singly linked list of integers forms a cycle or not.
A cycle in a linked list occurs when a node's next points back to a previous node in the ...read more
Ans. 
Detect if a singly linked list forms a cycle by checking if a node's next points back to a previous node.
• Traverse the linked list using two pointers, one moving one step at a time and the other moving two steps at a time.

• If the two pointers meet at any point, it indicates the presence of a cycle in the linked list.

• If one of the pointers reaches the end of the list (null), it means there is no cycle.
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Q2. 
Palindrome Partitioning II Problem Statement
Given a string ‘str’, find the minimum number of partitions needed such that every segment of the string is a palindrome.
The task is to make cuts in the stri...read more
Ans. 
Find the minimum number of partitions needed in a string such that every segment is a palindrome.
• Iterate through the string and check for palindromes at each possible partition point.

• Use dynamic programming to keep track of the minimum cuts needed.

• Consider edge cases where the string is already a palindrome or consists of different characters only.
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Round duration - 60 minutes
Round difficulty - Medium

Technical round that lasted for around 60 minutes. The interviewer asked questions related to data structures and algorithms.

Q1. 
DFS Traversal Problem Statement
Given an undirected and disconnected graph G(V, E), where V is the number of vertices and E is the number of edges, the connections between vertices are provided in the 'GR...read more
Ans. 
DFS traversal problem on an undirected and disconnected graph to find connected components.
• Perform Depth First Search (DFS) on each vertex to find connected components

• Use a visited array to keep track of visited vertices

• Print the number of connected components and list vertices in ascending order for each component
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Q2. 
Cycle Detection in Undirected Graph Problem Statement
You are provided with an undirected graph containing 'N' vertices and 'M' edges. The vertices are numbered from 1 to 'N'. Your objective is to determi...read more
Ans. 
Detect cycles in an undirected graph with given vertices and edges.
• Use Depth First Search (DFS) to traverse the graph and detect cycles.

• Maintain a visited array to keep track of visited vertices and a parent array to keep track of the parent of each vertex.

• If while traversing, you encounter a visited vertex that is not the parent of the current vertex, then a cycle exists.

• Consider edge cases like disconnected graphs an
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Round duration - 60 minutes
Round difficulty - Medium

Technical round that lasted for around 60 minutes. The interviewer asked questions related to data structures and algorithms.

Q1. 
Merge Sort Problem Statement
You are given a sequence of numbers, ARR. Your task is to return a sorted sequence of ARR in non-descending order using the Merge Sort algorithm.
Explanation:
The Merge Sort...read more
Ans. 
Implement Merge Sort algorithm to sort a sequence of numbers in non-descending order.
• Implement the Merge Sort algorithm using a Divide and Conquer approach

• Recursively divide the input array into two halves until the size of each array is 1

• Merge the sorted halves to produce a completely sorted array

• Ensure the output is in non-descending order
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Q2. 
Maximum Difference Problem Statement
Given an array ARR of N elements, your task is to find the maximum difference between any two elements in ARR.
If the maximum difference is even, print EVEN; if it is...read more
Ans. 
Find the maximum difference between any two elements in an array and determine if it is even or odd.
• Iterate through the array to find the maximum and minimum elements

• Calculate the difference between the maximum and minimum elements

• Check if the difference is even or odd and return the result
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Q3. What is hashing and how can it be implemented?
Ans. 
Hashing is a process of converting input data into a fixed-size string of bytes using a hash function.
• Hashing is used to securely store passwords by converting them into a hash value before storing in a database.

• Hashing is used in data structures like hash tables to quickly retrieve data based on a key.

• Common hash functions include MD5, SHA-1, and SHA-256.

• Hashing can be implemented in programming languages like Python
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Round duration - 60 minutes
Round difficulty - Easy

Technical Interview round where the interviewer asked questions based on Data structures and algorithms.

Q1. 
Reverse Linked List Problem Statement
Given a Singly Linked List of integers, your task is to reverse the Linked List by altering the links between the nodes.
Input:
The first line of input is an intege...read more
Ans. 
Reverse a singly linked list by altering the links between nodes.
• Iterate through the linked list and reverse the links between nodes.

• Use three pointers to keep track of the current, previous, and next nodes.

• Update the links between nodes to reverse the list.

• Return the head of the reversed linked list.
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Q2. 
Dijkstra's Shortest Path Problem
Given an undirected graph with ‘V’ vertices (labeled 0, 1, ... , V-1) and ‘E’ edges, where each edge has a weight representing the distance between two connected nodes (X,...read more
Ans. 
Dijkstra's algorithm is used to find the shortest path from a source node to all other nodes in a graph with weighted edges.
• Implement Dijkstra's algorithm to find the shortest path distances from the source node to all other nodes.

• Use a priority queue to efficiently select the next node with the shortest distance.

• Update the distances of neighboring nodes based on the current node's distance and edge weights.

• Handle disc...read more
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Round duration - 60 minutes
Round difficulty - Easy

Technical Interview round where the interviewer asked questions based on Data structures and algorithms.

Q1. 
Sort Linked List Based on Actual Values
Given a Singly Linked List of integers that are sorted based on their absolute values, the task is to sort the linked list based on the actual values.
The absolute...read more
Ans. 
Sort a Singly Linked List based on actual values instead of absolute values.
• Traverse the linked list and store the values in an array.

• Sort the array based on actual values.

• Update the linked list with the sorted values.
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Q2. 
Kth Largest Element Problem
Given an array containing N distinct positive integers and a number K, determine the Kth largest element in the array.
Example:
Input:
N = 6, K = 3, array = [2, 1, 5, 6, 3, ...read more
Ans. 
Find the Kth largest element in an array of distinct positive integers.
• Sort the array in non-increasing order to easily find the Kth largest element.

• Ensure all elements in the array are distinct for accurate results.

• Handle multiple test cases efficiently by iterating through each case.
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Round duration - 30 minutes
Round difficulty - Easy

HR Round that lasted for around 30 minutes. The interviewer asked questions to know more about me.

Round duration - 45 minutes
Round difficulty - Easy

This was a technical interview round.

Q1. How does AJAX work?
Ans. 
AJAX allows web pages to be updated asynchronously by exchanging data with a web server behind the scenes.
• AJAX stands for Asynchronous JavaScript and XML.

• It allows web pages to update content without reloading the entire page.

• AJAX uses XMLHttpRequest object to send and receive data from a server.

• Commonly used in web applications to provide a more responsive user experience.
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Q2. What is the difference between SOAP and REST?
Ans. 
SOAP is a protocol, while REST is an architectural style for web services.
• SOAP is a protocol that uses XML for message format and relies on a request-response model.

• REST is an architectural style that uses standard HTTP methods like GET, POST, PUT, DELETE.

• SOAP is more rigid and requires more bandwidth, while REST is lightweight and flexible.

• SOAP has built-in security features like WS-Security, while REST relies on exte...read more
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Q3. What is the difference between GET and POST methods in APIs?
Ans. 
GET is used to request data from a server, while POST is used to submit data to a server.
• GET requests data from a specified resource, while POST submits data to be processed to a specified resource.

• GET requests are cached by browsers, while POST requests are not.

• GET requests can be bookmarked and shared, while POST requests cannot.

• GET requests have length restrictions, while POST requests do not.

• Example: Using GET to r...read more
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Q4. What is the Observer Pattern?
Ans. 
The Observer Pattern is a behavioral design pattern where an object (subject) maintains a list of dependents (observers) that are notified of any state changes.
• Allows for one-to-many dependency between objects

• When the subject's state changes, all observers are automatically notified and updated

• Commonly used in event handling systems and GUI frameworks
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Round duration - 40 minutes
Round difficulty - Easy

This was the second technical interview round.

Q1. What is a singleton class?
Ans. 
A singleton class is a class that can only have one instance created throughout the entire application.
• Singleton classes have a private constructor to prevent multiple instances from being created.

• They typically provide a static method to access the single instance.

• Commonly used for logging, database connections, and configuration settings.
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Q2. What is meant by immutability in Java?
Ans. 
Immutability in Java refers to the property of objects whose state cannot be changed once they are created.
• Immutability ensures that once an object is created, its state cannot be modified.

• Immutable objects are thread-safe and can be shared without the risk of data corruption.

• String class in Java is an example of an immutable class.

• To create an immutable class, make the class final, all fields private, and provide only
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Q3. What is dependency injection?
Ans. 
Dependency injection is a design pattern where components are given their dependencies rather than creating them internally.
• Allows for easier testing by providing mock dependencies

• Promotes loose coupling between components

• Improves code reusability and maintainability

• Examples: Constructor injection, Setter injection, Interface injection
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Q4. How do you create an immutable class in Java?
Ans. 
To create an immutable class in Java, make the class final, make all fields private and final, provide only getter methods, and do not provide any setter methods.
• Make the class final to prevent inheritance.

• Make all fields private and final to prevent modification.

• Provide only getter methods to access the fields.

• Do not provide any setter methods to modify the fields.
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Round duration - 30 minutes
Round difficulty - Easy

HR round with typical behavioral problems.

Round duration - 60 minutes
Round difficulty - Easy

Technical Interview round with questions on DSA.

Q1. 
Stock Buy and Sell Problem Statement
You are given an array of integers PRICES where PRICES[i] represents the price of a stock on the i-th day, and an integer K representing the number of transactions you...read more
Ans. 
Determine maximum profit with at most K transactions by buying and selling stocks on given days.
• Iterate through the array of prices while keeping track of the maximum profit achievable with at most K transactions.

• Use dynamic programming to store the maximum profit at each day and transaction count.

• Consider buying and selling stocks at each day to calculate the maximum profit.

• Return the maximum profit achievable with at
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Q2. 
Sorted Order Printing of a BST Array
Given a Binary Tree consisting of 'N' nodes with integer values, your task is to determine the in-order traversal of the Binary Tree.
Input:
The first line contains ...read more
Ans. 
The task is to determine the in-order traversal of a Binary Tree given in level order.
• Implement a function to perform in-order traversal of a Binary Tree

• Use recursion to traverse left subtree, visit root, and then traverse right subtree

• Handle null nodes denoted by -1 in the input
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Round duration - 30 minutes
Round difficulty - Easy

HR round with typical behavioral problems.