American Express Software Developer Intern Interview Questions and Answers

Round duration - 90 minutes
Round difficulty - Medium

It consist three question - first que is of related to tree and i gave difficulty level of this question as hard. second que is of based on logical and reasoning , it is medium level question and third que can be done by map and it is also medium level que.
In codility platform we are not able to see hidden test cases whether it is satisfied or not . we just have to submit after passing sample testcases.

Q1. 
Minimum Number of Swaps to Sort an Array
Find the minimum number of swaps required to sort a given array of distinct elements in ascending order.
Input:
T (number of test cases)
For each test case:
N (siz...read more
Ans. 
The minimum number of swaps required to sort a given array of distinct elements in ascending order.
• Use a graph-based approach to find cycles in the array

• Count the number of swaps needed to fix each cycle

• Sum up the swaps needed for all cycles to get the total minimum swaps
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Q2. 
Maximum Non-Adjacent Subsequence Sum
Given an array of integers, determine the maximum sum of a subsequence without choosing adjacent elements in the original array.
Input:
The first line consists of an...read more
Ans. 
Find the maximum sum of a subsequence without choosing adjacent elements in an array.
• Use dynamic programming to keep track of the maximum sum at each index, considering whether to include or exclude the current element.

• At each index, the maximum sum is either the sum of the current element and the sum two positions back, or the sum at the previous index.

• Iterate through the array and update the maximum sum accordingly.

• E...read more
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Q3. 
Left View of a Binary Tree Problem Statement
Given a binary tree, your task is to print the left view of the tree.
Example:
Input:
The input will be in level order form, with node values separated by a...read more
Ans. 
Print the left view of a binary tree given in level order form.
• Traverse the tree level by level and print the first node encountered at each level

• Use a queue to perform level order traversal

• Keep track of the current level and the maximum level seen so far
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Round duration - 30 minutes
Round difficulty - Medium

basically this round is just same as HR round . they asked me behavioural questions and about my projects , hackathon. the timing is mid noon and interviewer is supportive , it makes first comfortable then start questioning . for this round i suggest be honest , don't just express your qualities but trying to show them by your skills and work.

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. 
Implement a function to find maximum elements for each contiguous subarray of size K in an array of integers.
• Iterate through the array and maintain a deque to store the indices of elements in decreasing order.

• Pop elements from the deque that are out of the current window and add the maximum element to the result array.

• Return the result array containing maximum elements for each subarray of size K.
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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. 
Find the length of the longest substring with at most K distinct characters in a given string.
• Use a sliding window approach to keep track of the characters and their counts in the substring.

• Maintain a hashmap to store the characters and their frequencies within the window.

• Update the window size and characters count as you iterate through the string.

• Keep track of the longest substring length with at most K distinct char...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:
...read more
Ans. 
Implement a stack using two queues to store integer values with specified functions.
• Use two queues to simulate stack operations efficiently.

• Maintain one queue for storing elements and another for temporary storage during push operation.

• Ensure proper handling of edge cases like empty stack or invalid operations.

• Example: Push operation involves transferring elements from one queue to another before adding the new element...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. 
Detect and remove loop in a singly linked list in place with O(n) time complexity and O(1) space complexity.
• Use Floyd's Cycle Detection Algorithm to identify the loop in the linked list.

• Once the loop is detected, use two pointers to find the start of the loop.

• Adjust the pointers to remove the loop and return the modified linked list.
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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. 
Find the intersections of two sorted lists of closed intervals.
• Iterate through both interval lists to find intersections

• Compare the intervals and find the common range

• Handle cases where there is no intersection between intervals
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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. 
Find the length of the longest switching subarray in a given array of positive integers.
• Iterate through the array and keep track of the longest switching subarray found so far.

• Check if the numbers at even and odd positions are identical to determine a switching subarray.

• Return the length of the longest switching subarray.

• Example: For input [1, 4, 1, 4, 3, 2, 3, 0], the longest switching subarray is [1, 4, 1, 4] with le...read more
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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. 
The task is to find the minimum number of deletions needed in a string to ensure each character appears a unique number of times.
• Iterate through the string and count the frequency of each character

• Track the frequencies in a hashmap

• Identify the characters with duplicate frequencies and calculate the minimum deletions needed

• Return the minimum number of deletions for each test case
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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. 
Check if a singly linked list is a palindrome by comparing elements from both ends.
• Traverse the linked list to find the middle point

• Reverse the second half of the linked list

• Compare the first half with the reversed second half to check for palindrome

• Example: Input: 1 2 3 2 1 -1, Output: true
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Q1. 
Travelling Salesman Problem
Given a list of cities numbered from 0 to N-1 and a matrix DISTANCE consisting of 'N' rows and 'N' columns, representing the distances between each pair of cities, find the sho...read more
Ans. 
The Traveling Salesman Problem seeks the shortest route visiting each city once and returning to the start.
• Brute Force Approach: Check all permutations of cities to find the shortest path, but this is inefficient for larger N.

• Dynamic Programming: Use bitmasking to represent visited cities and memoization to store results, reducing time complexity.

• Example: For cities 0, 1, 2 with distances 0-10-15, the optimal route is ...read more
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