Flipkart Software Developer Interview Questions, Process, and Tips

Round duration - 60 Minutes
Round difficulty - Medium

The round was held on Google Meet and I was given 2 coding problems for which first I had to explain my approach and then I had to write code in Shared Google Docs and dry run on sample test cases and discuss Time and Space Complexity.

Q1. 
Validate BST Problem Statement
Given a binary tree with N nodes, determine whether the tree is a Binary Search Tree (BST). If it is a BST, return true; otherwise, return false.
A binary search tree (BST)...read more
Ans. 
Validate if a given binary tree is a Binary Search Tree (BST) or not.
• Check if the left subtree of a node contains only nodes with data less than the node's data.

• Check if the right subtree of a node contains only nodes with data greater than the node's data.

• Recursively check if both left and right subtrees are also binary search trees.
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Q2. 
Maximum Sum Path from Leaf to Root
Given a binary tree with 'N' nodes, identify the path from a leaf node to the root node that has the maximum sum among all root-to-leaf paths.
Example:
All the possibl...read more
Ans. 
Find the path from a leaf node to the root node with the maximum sum in a binary tree.
• Traverse the binary tree from leaf to root while keeping track of the sum of each path.

• Compare the sums of all paths and return the path with the maximum sum.

• Use recursion to traverse the tree efficiently and keep updating the maximum sum path.
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Round duration - 60 Minutes
Round difficulty - Medium

This was also a Data Structures and Algorithms round where I was asked to solve 2 coding problems explaining my approach with proper Complexity Analysis . After the coding questions were over there was some time left so the interviewer asked me some concepts related to DBMS.

Q1. 
Next Permutation Problem Statement
You are given a permutation of 'N' integers. A sequence of 'N' integers is considered a permutation if it includes all integers from 1 to 'N' exactly once. Your task is ...read more
Ans. 
The task is to rearrange a given permutation of 'N' integers to form the lexicographically next greater permutation.
• Iterate from right to left to find the first element that is smaller than the element to its right.

• Swap this element with the smallest element to its right that is greater than it.

• Reverse the elements to the right of the swapped element to get the lexicographically next greater permutation.
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Q2. 
Largest BST Subtree Problem Statement
You are given a binary tree with 'N' nodes. Your task is to determine the size of the largest subtree within the binary tree which is also a Binary Search Tree (BST).
...read more
Ans. 
Find the size of the largest subtree in a binary tree that is also a Binary Search Tree.
• Traverse the tree in a bottom-up manner to check if each subtree is a BST.

• Keep track of the size of the largest BST subtree encountered so far.

• Use recursion to solve this problem efficiently.

• Example: For the input 1 2 3 4 -1 5 6 -1 7 -1 -1 -1 -1 -1 -1, the largest BST subtree has a size of 3.
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Q3. Can you explain indexing in databases?
Ans. 
Indexing in databases is a technique used to improve the speed of data retrieval by creating a data structure that allows for quick lookups.
• Indexes are created on columns in a database table to speed up the retrieval of rows that match a certain condition.

• Types of indexes include B-tree, hash, and bitmap indexes.

• Indexes can improve the performance of SELECT queries but may slow down INSERT, UPDATE, and DELETE operation...read more
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Round duration - 50 Minutes
Round difficulty - Medium

This round also had 2 questions related to DS and Algo . One was from graphs and the other was an implementation of a LRU Cache . There were 2 interviewers and both of them were quite friendly and helpful. Overall, this round went well.

Q1. 
Detect Cycle in a Directed Graph
You are provided with a directed graph composed of 'N' nodes. You have a matrix called 'EDGES' with dimensions M x 2, which specifies the 'M' edges in the graph. Each edge...read more
Ans. 
Detect cycle in a directed graph using depth-first search (DFS) algorithm.
• Use DFS to traverse the graph and detect back edges (edges that point to an ancestor node).

• Maintain a visited array to keep track of visited nodes and a recursion stack to keep track of nodes in the current path.

• If a back edge is found during traversal, a cycle exists in the graph.

• Return true if a cycle is detected, false otherwise.
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Q2. 
LRU Cache Design Question
Design a data structure for a Least Recently Used (LRU) cache that supports the following operations:
1. get(key) - Return the value of the key if it exists in the cache; otherw...read more
Ans. 
Design a Least Recently Used (LRU) cache data structure that supports get and put operations with capacity constraint.
• Use a combination of hashmap and doubly linked list to efficiently implement the LRU cache.

• Keep track of the least recently used item and update it accordingly when inserting new items.

• Ensure to handle the capacity constraint by evicting the least recently used item when the cache is full.

• Implement get(...read more
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Round duration - 60 Minutes
Round difficulty - Medium

This was a typical DS/Algo where I was asked to solve two questions related to Binary Trees and write the pseudo code for both of them followed by some theoretical questions related to Operating Systems.

Q1. 
K-th Largest Number in a BST
Given a binary search tree (BST) consisting of integers and containing 'N' nodes, your task is to find and return the K-th largest element in this BST.
If there is no K-th la...read more
Ans. 
Find the K-th largest element in a BST.
• Perform reverse in-order traversal of the BST to find the K-th largest element.

• Keep track of the count of visited nodes to determine the K-th largest element.

• Return -1 if there is no K-th largest element in the BST.
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Q2. 
Is Height Balanced Binary Tree Problem Statement
Determine if the given binary tree is height-balanced. A tree is considered height-balanced when:
1. The left subtree is balanced.
2. The right subtree is bala...read more
Ans. 
Determine if a given binary tree is height-balanced by checking if left and right subtrees are balanced and their height difference is at most 1.
• Check if the left subtree is balanced

• Check if the right subtree is balanced

• Calculate the height difference between the left and right subtrees

• Return 'True' if all conditions are met, otherwise return 'False'
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Q3. Can you explain the concepts of Zombie Process and Orphan Process in operating systems?
Ans. 
Zombie process is a terminated process that has completed execution but still has an entry in the process table. Orphan process is a process whose parent process has terminated.
• Zombie process is created when a child process completes execution but its parent process has not yet read its exit status.

• Zombie processes consume system resources and should be cleaned up by the parent process using wait() system call.

• Orphan p...read more
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Round duration - 60 Minutes
Round difficulty - Medium

This was also a Data Structures and Algorithm round where I was asked to solve 3 medium to hard level problems along with their pseudo code within 60 minutes .

Q1. 
Longest Substring Without Repeating Characters Problem Statement
Given a string S of length L, determine the length of the longest substring that contains no repeating characters.
Example:
Input:
"abac...read more
Ans. 
Find the length of the longest substring without repeating characters in a given string.
• Use a sliding window approach to keep track of the longest substring without repeating characters.

• Use a hashmap to store the index of each character in the string.

• Update the start index of the window when a repeating character is found.

• Calculate the maximum length of the window as you iterate through the string.

• Return the maximum le
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Q2. 
Problem: Search In Rotated Sorted Array
Given a sorted array that has been rotated clockwise by an unknown amount, you need to answer Q queries. Each query is represented by an integer Q[i], and you must ...read more
Ans. 
Search for integers in a rotated sorted array efficiently.
• Use binary search to efficiently search for integers in the rotated sorted array.

• Handle the rotation of the array while performing binary search.

• Return the index of the integer if found, else return -1.
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Q3. 
Count Subarrays with Sum Divisible by K
Given an array ARR and an integer K, your task is to count all subarrays whose sum is divisible by the given integer K.
Input:
The first line of input contains an...read more
Ans. 
Count subarrays with sum divisible by K in an array.
• Iterate through the array and keep track of the prefix sum modulo K.

• Use a hashmap to store the frequency of each prefix sum modulo K.

• For each prefix sum, increment the count by the frequency of (prefix sum - K) modulo K.

• Handle the case when prefix sum itself is divisible by K.

• Return the total count of subarrays with sum divisible by K.
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Round duration - 50 Minutes
Round difficulty - Medium

In this round , I was asked to code a simple question related to BST . After that I was asked the internal implementation of a Hash Map where I was supposed to design a Hash Map using any of the Hashing Algorithms that I know . This was preety challenging for me but I got to learn so much from it.

Q1. 
Ceil Value from BST Problem Statement
Given a Binary Search Tree (BST) and an integer, write a function to return the ceil value of a particular key in the BST.
The ceil of an integer is defined as the s...read more
Ans. 
Ceil value of a key in a Binary Search Tree (BST) is found by returning the smallest integer greater than or equal to the given number.
• Traverse the BST to find the closest value greater than or equal to the key.

• Compare the key with the current node value and update the ceil value accordingly.

• Recursively move to the left or right subtree based on the comparison.

• Return the ceil value once the traversal is complete.
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Q2. 
Design a Constant Time Data Structure
Create a data structure that maintains mappings between keys and values, supporting the following operations in constant time:
1. INSERT(key, value): Add or update t...read more
Ans. 
Design a constant time data structure to maintain mappings between keys and values with various operations.
• Use a hash table to achieve constant time complexity for INSERT, DELETE, SEARCH, and GET operations.

• Keep track of the number of key-value pairs for GET_SIZE operation.

• Check if the hash table is empty for IS_EMPTY operation.

• Return true or false for SEARCH operation based on key existence.

• Return the value associated...read more
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Round duration - 90 Minutes
Round difficulty - Hard

I found the online coding round of Flipkart to be quite difficult based on the constraints of the problem and their time limits. I coded the first problem quite easily but on the second and the third problem , my code could only pass a few test cases and gave TLE for most of them. Both the questions required very efficient solution and the last 5 to 10 Test Cases carried more weight than the rest so I didn't get through this round.

Q1. 
Print the Kth Digit
Given three non-negative integers N, M, and K, compute the Kth digit from the right in the number obtained from N raised to the power M (i.e., N ^ M).
Input:
The first line contains ...read more
Ans. 
The task is to find the Kth digit from the right in the number obtained from N raised to the power M.
• Iterate through the digits of N^M from right to left

• Keep track of the position of the current digit

• Return the digit at position K from the right
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Q2. 
The Skyline Problem
Compute the skyline of given rectangular buildings in a 2D city, eliminating hidden lines and forming the outer contour of the silhouette when viewed from a distance. Each building is ...read more
Ans. 
Compute the skyline of given rectangular buildings in a 2D city, eliminating hidden lines and forming the outer contour of the silhouette.
• Iterate through the buildings and create a list of critical points (x, y) where the height changes.

• Sort the critical points based on x-coordinate and process them to form the skyline.

• Merge consecutive horizontal segments of equal height into one to ensure no duplicates.

• Return the fin...read more
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Q3. 
Longest Palindromic Substring Problem Statement
You are provided with a string STR of length N. The goal is to identify the longest palindromic substring within this string. In cases where multiple palind...read more
Ans. 
Identify the longest palindromic substring in a given string.
• Iterate through the string and expand around each character to find palindromes

• Keep track of the longest palindrome found

• Return the longest palindrome with the smallest start index
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