Walmart SDE-2 Interview Questions, Process, and Tips

Round duration - 30 Minutes
Round difficulty - Easy

MCQ Challenge was to test basic computer fundamentals. The quiz had 30 questions to be attempted in 25 minutes consisting questions related to Data structures and algorithm, OOPS, OS, DBMS and some questions to find the output of Java Program.
Platform was fast and responsive, and we were not allowed to switch through tabs during the test.

Q1. 
Maximum Depth of a Binary Tree Problem Statement
Given the root node of a binary tree with N nodes, where each node contains integer values, determine the maximum depth of the tree. The depth is defined a...read more
Ans.  Recursive approach
The idea is to use DFS (Depth First Search) traversal and recursively find the maximum depths of the left subtree and right subtree, returning the max of both the values plus 1 (counting the root node) as our answer.
 
• We are given a function ‘findMaxDepth’ which takes the root node of the binary tree “ROOT”  as the parameter and returns an integer which is the maximum depth of the binary tre...read more
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Round duration - 90 minutes
Round difficulty - Hard

90 minutes is what we get to present a logical coding solution to the challenge presented to us. There were 2 coding questions and we can submit the answer as many times we want. There were hidden test cases and after submitting we could only see the score.

Q1. 
Sliding Window Maximum Problem Statement
You are given an array/list of integers with length 'N'. A sliding window of size 'K' moves from the start to the end of the array. For each of the 'N'-'K'+1 possi...read more
Ans. Brute Force
Our intuition here is to go through each sliding window and keep track of the maximum element in each sliding window. To implement the same we run two nested loops, where the outer loop which will mark the starting point of the subarray of length k, the inner loop will run from the starting INDEX to INDEX + K, K elements from starting index and store the maximum element among these K elements into the answer...read more
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Q2. 
String Transformation Problem
Given a string (STR) of length N, you are tasked to create a new string through the following method:
Select the smallest character from the first K characters of STR, remov...read more
Ans. Brute Force Approach
• Create a new “answer” string that will contain the modified string
• While the input string's length is greater than 0
  • Find the minimum character in the first K characters of the string (or the entire string if its length is less than K)
  • Append that character to the “answer” string
  • Remove that character from the input string
• Return the “answer” string
Space Complexity: O(1)Explanation:
O(1)
 
Since we ar...read more
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Round duration - 40 Minutes
Round difficulty - Medium

It was the first technical round conducted on Zoom held for about 40 min. The video was enabled for this round. Computer fundamentals and problem solving was checked in this round.

Q1. 
Maximum Number With Single Swap
You are given an array of N elements that represent the digits of a number. You can perform one swap operation to exchange the values at any two indices. Your task is to de...read more
Ans. Brute Force
The idea is to generate all the possible numbers by trying all the possible combinations of indices. We will run two nested loops to generate all numbers and inside the inner loop with we will have to compare the array, we get after swapping with the maximum number we get till this step.
1. Let’s say we have a given array ARR.
2. Let’s take an integer array of size N say MAX initialized to ARR, MAX[N] = ARR.
3. Iterate ...read more
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Q2. 
Equilibrium Index Problem Statement
Given an array Arr consisting of N integers, your task is to find the equilibrium index of the array.
An index is considered as an equilibrium index if the sum of elem...read more
Ans. Brute Force
• We can try the brute force approach in which we consider every index starting from 0 as a possible candidate for equilibrium index, and to check if it is really an equilibrium index, we can calculate the sum of elements on both sides of that index, and check if they are equal or not. equal or not.
• Let us initialise the ans = -1, which will contain our valid index.
• Since index 0 and n - 1 cannot be possible can...read more
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Round duration - 30 Minutes
Round difficulty - Easy

It was the first technical round conducted on Zoom held for about 40 min. The video was enabled for this round.

Q1. 
Maximum Frequency Number Problem Statement
Given an array of integers with numbers in random order, write a program to find and return the number which appears the most frequently in the array.
If multip...read more
Ans. Brute Force Approach
Here, we can simply run two loops. The outer loop picks all elements one by one and the inner loop finds the frequency of the picked element and compares it with the maximum present so far.
 
Algorithm:
 
• Declare 4 variables as ‘maxFrequency’ , ‘currentFrequency’ , ‘maxElement’ , ‘currentElement’ and initialize them with 0
• Run a loop from ‘i’ = ‘0’ to ‘N’
  • Set ‘currentElement’ as arr[i] and ‘curr...read more
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Round duration - 30 Minutes
Round difficulty - Easy

This was the final round held for about 30 min on Zoom. My video was enabled all the time and basic HR questions were being asked.

Round duration - 50 Minutes
Round difficulty - Medium

Standard Data Structures and Algorithms round . One has to be fairly comfortable in solving algorithmic problems to pass this round with ease.

Q1. 
Pair Sum Problem Statement
You are given an integer array 'ARR' of size 'N' and an integer 'S'. Your task is to find and return a list of all pairs of elements where each sum of a pair equals 'S'.
Note:
...read more
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Q2. 
Convert Sorted Array to BST Problem Statement
Given a sorted array of length N, your task is to construct a balanced binary search tree (BST) from the array. If multiple balanced BSTs are possible, you ca...read more
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Round duration - 50 Minutes
Round difficulty - Medium

Again a DSA specific round , where I was given two problems to solve ranging from Medium to Hard. Major topics discussed were Binary Trees and Dynamic Programming.

Q1. 
Top View of a Binary Tree Problem Statement
You are given a Binary Tree of integers. Your task is to determine and return the top view of this binary tree.
The top view of a binary tree consists of all th...read more
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Q2. 
Minimum Jumps Problem Statement
Bob and his wife are in the famous 'Arcade' mall in the city of Berland. This mall has a unique way of moving between shops using trampolines. Each shop is laid out in a st...read more
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Round duration - 50 Minutes
Round difficulty - Medium

This round majorly focused on past projects and experiences from my Resume and some standard System Design + LLD questions + some basic OS questions which a SDE-2 is expected to know .

Q1. Design a URL shortener.
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Q2. How can you print numbers from 1 to 100 using more than two threads in an optimized approach?
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Round duration - 60 Minutes
Round difficulty - Medium

Standard Data Structures and Algorithms round . One has to be fairly comfortable in solving algorithmic problems to pass this round with ease.

Q1. 
Minimum Cost to Connect Sticks
You are provided with an array, ARR, of N positive integers. Each integer represents the length of a stick. The task is to connect all sticks into one by paying a cost to jo...read more
Ans. 
It is a greedy approach where we will form a min-heap of all the lengths of sticks that are given to us. In this approach, we will always find two sticks with minimum length and connect them and add their cost to our answer. Also, we will add the newly formed stick back into our min-heap. And then we will continue to do the same procedure for all the remaining sticks. Since we need to minimize the cost to connect all t...read more
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Q2. 
Minimum Jumps Problem Statement
Bob and his wife are in the famous 'Arcade' mall in the city of Berland. This mall has a unique way of moving between shops using trampolines. Each shop is laid out in a st...read more
Ans. 
Approach 1 : Naive Recursive Approach

A naive approach is to start from the first element and recursively call for all the elements reachable from first
element. The minimum number of jumps to reach end from first can be calculated using minimum number of jumps
needed to reach end from the elements reachable from first.
minJumps(start, end) = Min ( minJumps(k, end) ) for all k reachable from start

TC : O(n^n)
SC:O(n)


Approach...read more
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Round duration - 70 Minutes
Round difficulty - Hard

This round was preety intense and went for over 1 hour . I was asked 2 preety good coding questions (one was from Graphs and the other one was from DP) . After that I was grilled on my Computer Networks concepts but luckily I was able to answer all the questions and the interviewer was also quite impressed .

Q1. 
Bipartite Graph Problem Statement
Determine if a given graph is bipartite. A graph is bipartite if its vertices can be divided into two independent sets, 'U' and 'V', such that every edge ('u', 'v') conne...read more
Ans. 
Algorithm : 
1) Create a graph such that there is a edge between each pair of enemies.
2) We need to find that the above graph is bipartite or not. Check whether the graph is 2-colorable or not
3) We can do that by running dfs and using an auxilary array col to store the assigned col of the node.
4) If we can color the graph with two color such that no two enemies have same color then only we can create two teams.

TC :...read more
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Q2. 
Maximum Length Pair Chain Problem Statement
You are provided with 'N' pairs of integers such that in any given pair (a, b), the first number is always smaller than the second number, i.e., a < b. A pai...read more
Ans. 
Approach 1 (Using DP ) :

Observe that , If a chain of length k ends at some pairs[i], and pairs[i][1] < pairs[j][0], we can extend this chain to a chain of length k+1

Steps :
1) Sort the pairs by first coordinate, and let dp[i] be the length of the longest chain ending at pairs[i]. 
2) When i < j and pairs[i][1] < pairs[j][0], we can extend the chain, and so we have the candidate answer 
dp[j] = max(dp[j]...read more
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Q3. Can you explain the TCP/IP protocol?
Ans. 
1) TCP or TCP/IP is the Transmission Control Protocol/Internet Protocol. 
2) It is a set of rules that decides how a computer connects to the Internet and how to transmit the data over the network. 
3) It creates a virtual network when more than one computer is connected to the network and uses the three ways handshake model to establish the connection which makes it more reliable.
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Q4. Can you explain the DHCP Protocol?
Ans. 
1) DHCP is the Dynamic Host Configuration Protocol.
2) It is an application layer protocol used to auto-configure devices on IP networks enabling them to use the TCP and UDP-based protocols.
3) The DHCP servers auto-assign the IPs and other network configurations to the devices individually which enables them to communicate over the IP network. 
4) It helps to get the subnet mask, IP address and helps to resolve the
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Round duration - 50 Minutes
Round difficulty - Medium

This round majorly focused on past projects and experiences from my Resume and some standard System Design +
LLD questions + some basic OS questions which a SDE-2 is expected to know .

Q1. How would you design a system like Pastebin?
Ans. 
Approach : 

Pastebin allows users to store text-based data over the internet for a set period of time and generate a unique URL corresponding uploaded data to share that with anyone. Users who create that data, can also modify it by logging in to the same account. 

Database Schema :

i) users(userID, name, createdAT, metaData)
ii) paste(pasteID, content, URL, createdAt, expiryAt)

Algorithm :

1) create_paste(api_key,...read more
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Q2. What is data abstraction and how can it be achieved?
Ans. 
Answer : 
1) Data abstraction is a very important feature of OOPs that allows displaying only the important information and hiding the implementation details. 
2) For example, while riding a bike, you know that if you raise the accelerator, the speed will increase, but you don’t know how it actually happens. 
3) This is data abstraction as the implementation details are hidden from the rider.

Data abstractio...read more
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