Paytm Software Developer Interview Questions, Process, and Tips

Round duration - 60 minutes
Round difficulty - Easy

2 DSA problems to be solved in 60 min time limit.

Q1. 
Next Greater Element Problem Statement
Given a list of integers of size N, your task is to determine the Next Greater Element (NGE) for every element. The Next Greater Element for an element X is the firs...read more
Ans. 
Given a list of integers, find the next greater element for each element in the list.
• Iterate through the list from right to left and use a stack to keep track of elements.

• Pop elements from the stack until a greater element is found or the stack is empty.

• Store the next greater element for each element in a result array.

• If no greater element is found, store -1 in the result array.
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Q2. 
Floor Value of X Problem Statement
Given a sorted array A and an integer X, your task is to find and return the floor value of X in the array.
The floor value of X is the largest element in array A which...read more
Ans. 
Find the largest element in a sorted array smaller than or equal to a given integer X.
• Use binary search to efficiently find the floor value of X in the sorted array.

• Compare the middle element of the array with X and adjust the search accordingly.

• Return the element before or equal to X as the floor value, or -1 if no such element exists.
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Round duration - 60 minutes
Round difficulty - Medium

Face to Face round with interviewer.

Q1. 
Longest Common Subsequence Problem Statement
Given two strings STR1 and STR2, determine the length of their longest common subsequence.
A subsequence is a sequence that can be derived from another sequen...read more
Ans. 
The task is to find the length of the longest common subsequence between two given strings.
• Implement a function to find the longest common subsequence between two strings.

• Use dynamic programming to solve this problem efficiently.

• Iterate through the strings and build a matrix to store the lengths of common subsequences.

• The value in the bottom-right corner of the matrix will be the length of the longest common subsequenc
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Q2. 
Maximum Subarray Sum Problem Statement
Given an array of integers, determine the maximum possible sum of any contiguous subarray within the array.
Example:
Input:
array = [34, -50, 42, 14, -5, 86]
Out...read more
Ans. 
Find the maximum sum of any contiguous subarray within an array of integers.
• Iterate through the array and keep track of the maximum sum of subarrays encountered so far.

• At each index, decide whether to include the current element in the subarray or start a new subarray.

• Update the maximum sum if a new maximum is found.

• Example: For array [34, -50, 42, 14, -5, 86], the maximum subarray sum is 137.
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Round duration - 60 minutes
Round difficulty - Medium

Face to Face DSA round.

Q1. 
Delete Middle Node Problem Statement
You are given a singly linked list of integers. The task is to delete the middle node of this list.
Note:
1. If the list has no middle node, return an empty list (NU...read more
Ans. 
Delete the middle node of a singly linked list in O(N) time complexity and O(1) space complexity.
• Identify the middle node using slow and fast pointers technique.

• Update the pointers to skip the middle node.

• Handle edge cases like no middle node or two middle nodes.

• Perform the deletion in a single traversal of the linked list.

• Return the modified linked list after deletion.
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Q2. 
Group Anagrams Together
Given an array/list of strings STR_LIST, group the anagrams together and return each group as a list of strings. Each group must contain strings that are anagrams of each other.
E...read more
Ans. 
Group anagrams together in a list of strings.
• Iterate through the list of strings and sort each string to group anagrams together.

• Use a hashmap to store the sorted string as key and the original string as value.

• Return the values of the hashmap as the grouped anagrams.
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Round duration - 60 minutes
Round difficulty - Easy

This round was with VP (technology). 
1. One DSA problem.
2. Had a discussion on the projects mentioned in CV.
3. Theory Ques from DBMS, OS.

Q1. 
Job Sequencing Problem Statement
You are provided with a N x 2 2-D array called Jobs consisting of N jobs. In this array, Jobs[i][0] represents the deadline of the i-th job, while Jobs[i][1] indicates the...read more
Ans. 
Maximize profit by scheduling jobs within their deadlines.
• Sort the jobs array in descending order of profits.

• Iterate through the sorted array and schedule jobs based on deadlines.

• Keep track of completed jobs and their profits to calculate the total profit.

• Return the maximum profit achieved by scheduling jobs within deadlines.
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Round duration - 75 minutes
Round difficulty - Easy

This round was conducted in Hackerrank portal for a total duration of 75 minutes and was divided into 4 sections.

1st Section : Aptitude Section : 14 questions , 28 minutes
2nd Section : Technical Section : 12 questions , 17 minutes
3rd Section :1 coding Questions : 20 minutes+30 minutes

This Round was Conducted on Hackerrank (Webcam Enabled).

Q1. 
Container with Most Water Problem Statement
Given a sequence of 'N' space-separated non-negative integers A[1], A[2], ..., A[i], ..., A[n], where each number in the sequence represents the height of a lin...read more
Ans. 
Find two lines to form a container with maximum water capacity based on given heights.
• Iterate through the array and use two pointers to find the maximum area.

• Calculate the area using the formula: min(height[left], height[right]) * (right - left).

• Move the pointer with the smaller height towards the center to potentially find a larger area.
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Q2. 
Maze Obstacle Problem Statement
Given an N * M grid representing a maze with obstacles, compute and return the total number of distinct paths from the top-left cell to the bottom-right cell. A cell in the...read more
Ans. 
Find the total number of distinct paths in a maze with obstacles from top-left to bottom-right cell.
• Use dynamic programming to keep track of the number of paths to reach each cell.

• Handle blocked cells by setting their path count to 0.

• Only move right or down from any given cell to calculate the number of paths.

• Return the total number of valid paths modulo 10^9 + 7.
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Round duration - 100 minutes
Round difficulty - Medium

This was an Online F2F Technical Round conducted on CodePair : Hackerrank. So, Basically You have to Run and Submit ( Pass All Test cases) in the Interview Round also (Like normal Coding Test) in Codepair : Hackerrank & along with that You should have to explain your Code and Approach to the Interviewers.
The Interviewers were helpful and didn't hesitate in giving hints.
Timing - 10:00 A.M to 12:00 P.M

Q1. 
Minimum Fountains Activation Problem
In this problem, you have a one-dimensional garden of length 'N'. Each position from 0 to 'N' has a fountain that can provide water to the garden up to a certain range...read more
Ans. 
Find the minimum number of fountains to activate to water the entire garden.
• Iterate through the array to find the coverage of each fountain.

• Keep track of the farthest coverage reached by each activated fountain.

• Activate the fountain that covers the farthest distance not yet covered.

• Repeat until the entire garden is watered.
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Q2. 
Minimize Cash Flow Problem
You are provided with a list of 'transactions' involving 'n' friends who owe each other money. Each entry in the list contains information about a receiver, sender, and the tran...read more
Ans. 
Minimize cash flow among friends by optimizing transactions.
• Create a graph where nodes represent friends and edges represent transactions.

• Calculate net amount each friend owes or is owed by summing up all transactions.

• Use a recursive algorithm to minimize cash flow by settling debts between friends.

• Update the graph after each settlement and continue until all debts are settled.

• Output the minimized cash flow in a 2-D ma
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Round duration - 30 minutes
Round difficulty - Easy

This was a Telephonic Round (Audio Call). The HR was friendly and asked basic questions.
The timing was 2:00 PM to 2:30 PM.

Round duration - 60 Minutes
Round difficulty - Easy

Q1. 
Lexicographically Smallest Array Problem Statement
You are given an array ARR of 'N' integers and a positive integer 'K'.
Your task is to determine the lexicographically smallest array that can be obtain...read more
Ans. 
The task is to determine the lexicographically smallest array that can be obtained by performing at most 'K' swaps of consecutive elements.
• Sort the array in non-decreasing order and keep track of the number of swaps made.

• Iterate through the array and swap adjacent elements if it results in a lexicographically smaller array.

• Continue swapping until the maximum number of swaps 'K' is reached or the array is lexicographica...read more
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Round duration - 20 Minutes
Round difficulty - Easy

Round duration - 70 minutes
Round difficulty - Easy

The first round was the Online Coding Round of 70 minutes with 3 problems of 3 marks, 3 marks, and 4 marks respectively.
The first two questions were easy and the third one was a bit tricky. The round started at 6 PM. 
Anyone who is practicing continuously could have solved these questions easily within the time limit. The test cases were also not so hard and distinct. I coded in C++ language.
The questions asked were-
1. Minimum insertions required to make a string palindrome
2. To find the distance of the closest leaf from a node with given data.
3. Add two numbers represented by linked lists

22 students were selected for the next round.

Q1. 
Minimum Insertions to Make a String Palindrome
Determine the minimal number of characters needed to insert into a given string STR to transform it into a palindrome.
Example:
Input:
STR = "abcaa"
Outp...read more
Ans. 
The task is to find the minimum number of characters needed to insert into a given string to make it a palindrome.
• Use dynamic programming to find the longest palindromic subsequence of the given string.

• Subtract the length of the longest palindromic subsequence from the length of the original string to get the minimum insertions required.

• Handle edge cases like an empty string or a string that is already a palindrome.

• Exa...read more
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Q2. 
Closest Leaf in a Binary Tree
Ninja is stuck in a maze represented as a binary tree, and he is at a specific node ‘X’. Help Ninja find the shortest path to the nearest leaf node, which is considered an ex...read more
Ans. 
Find the minimum distance from a given node to the nearest leaf node in a binary tree.
• Traverse the binary tree from the given node 'X' to find the nearest leaf node using BFS or DFS.

• Keep track of the distance from 'X' to each leaf node encountered during traversal.

• Return the minimum distance found as the output.
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Q3. 
Adding Two Linked Lists
Given two singly linked lists, with each list representing a positive number without leading zeros, your task is to add these two numbers and return the result in the form of a new...read more
Ans. 
Add two numbers represented by linked lists and return the result as a new linked list.
• Traverse both linked lists simultaneously while adding corresponding elements and carry over the sum if needed

• Handle cases where one linked list is longer than the other

• Create a new linked list to store the sum of the two numbers
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Round duration - 80 minutes
Round difficulty - Easy

It was a technical interview. The platform used was google meet for online video calling. The interviewer first introduced himself then asked me to introduce myself. He also asked about my well-being amid the Covid-19 pandemic. He asked me 3 problems from data structures. He put a lot of focus on my project. We discussed about my project for about 20 mins. He asked various questions related to my project and I answered them confidently. After 70-75 mins he said that interview was over and that I may ask him anything. I asked him to give me feedback about my resume and my project. He gave me advice to improve my resume and the interview was over. The first technical interview was easy and was not so challenging as I was prepared.

Q1. 
All Pairs with Target Sum
Given an array of integers ARR with length 'N' and an integer 'Target', the task is to find all unique pairs of elements that add up to the 'Target'.
Input:
First line: Integer...read more
Ans. 
Find all unique pairs of elements in an array that add up to a given target sum.
• Use a hashmap to store the difference between the target sum and each element as keys and their indices as values.

• Iterate through the array and check if the current element's complement exists in the hashmap.

• Return the pairs of elements that add up to the target sum.
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Q2. 
Quick Sort Problem Statement
Sort the given array of integers in ascending order using the quick sort algorithm. Quick sort is a divide-and-conquer algorithm where a pivot point is chosen to partition the...read more
Ans. 
Implement quick sort algorithm to sort an array of integers in ascending order.
• Choose a pivot element (e.g., rightmost element) to partition the array into two subarrays.

• Recursively apply quick sort on the subarrays until the entire array is sorted.

• Time complexity can be optimized to NlogN for worst-case scenarios.
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Q3. 
Merge Sort Task
Given a sequence of numbers, denoted as ARR, your task is to return a sorted sequence of ARR in non-descending order using the Merge Sort algorithm.
Example:
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 which involves dividing the array into two halves, sorting each half, and then merging them back together.

• Recursively call the Merge Sort function on each half of the array until the base case of having a single element in the array is reached.

• Merge the sorted halves back together in a new array in no...read more
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Round duration - 60 minutes
Round difficulty - Medium

This was also a technical round. The interviewer focused on data structures and resume. Apart from some basic questions about my resume, he asked majorly about data structures and algorithms. The interview was an hour long and he asked only 2 problems. Both of them were from trees. In this round, he focused if I can change my approach if a slight change is made in the question. Like he asked me to write code for inorder traversal. Obviously, I used a recursive approach. He then asked me to use the iterative method to find inorder traversal of the tree.

The questions he asked were-
1. Inorder traversal (both recursive and iterative method)
2. Level Order Traversal
( For obvious reasons I knew level order traversal very well. I coded it swiftly, so he asked me to write code for Zig-Zag traversal)

Q1. 
Inorder Successor in a Binary Tree
Find the inorder successor of a given node in a binary tree. The inorder successor is the node that appears immediately after the given node during an inorder traversal....read more
Ans. 
Find the inorder successor of a given node in a binary tree.
• Perform an inorder traversal of the binary tree to find the successor of the given node.

• If the given node has a right child, the successor will be the leftmost node in the right subtree.

• If the given node does not have a right child, backtrack to the parent nodes to find the successor.
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Q2. 
Zigzag Traversal of Binary Tree
Given a binary tree with integer values in its nodes, your task is to print the zigzag traversal of the tree.
Note:
In zigzag order, level 1 is printed from left to right...read more
Ans. 
Implement a function to print the zigzag traversal of a binary tree.
• Use a queue to perform level order traversal of the binary tree.

• Maintain a flag to switch between printing nodes from left to right and right to left at each level.

• Store nodes at each level in a list and reverse the list if the flag is set to print in zigzag order.
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Round duration - 50 minutes
Round difficulty - Medium

This was the final round of the Interview process. My interview was scheduled for 7.30 PM. It started at approximately 7.40 PM. The main focus of the interviewer was on my projects and my skills. He asked me many questions regarding my project like what problems I faced, what did you learn from this, apart from developing skills what else did you learn while developing the project, why did you use this tech instead of this, security features, scalability of the project and many more. I answered almost every question as perfectly as I can. Later he asked me some basic questions from NodeJS (as I am a full stack developer). In the end, he asked a puzzle. I didn't know the solution to the puzzle but we discussed it and I figured out the solution.

Round duration - 70 minutes
Round difficulty - Medium

Timing: 6:00 pm
3 coding questions of medium to be solved in 70 minutes.

Q1. 
Maximum Subarray Sum Problem Statement
Given an array of numbers, the task is to find the maximum sum of any contiguous subarray of the array.
Input:
The first line of input contains the size of the arr...read more
Ans. 
Find the maximum sum of any contiguous subarray in an array of numbers in O(N) time.
• Use Kadane's algorithm to find the maximum subarray sum in O(N) time.

• Initialize two variables: maxEndingHere and maxSoFar to keep track of the maximum sum.

• Iterate through the array and update the variables accordingly.

• Return the maxSoFar as the result.
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Q2. 
Closest Leaf in a Binary Tree
Ninja is stuck in a maze represented as a binary tree, and he is at a specific node ‘X’. Help Ninja find the shortest path to the nearest leaf node, which is considered an ex...read more
Ans. 
Find the minimum distance from a given node to the nearest leaf node in a binary tree.
• Traverse the binary tree from the given node 'X' to find the nearest leaf node.

• Use a queue for level order traversal to efficiently find the nearest leaf node.

• Calculate the distance from node 'X' to each leaf node and return the minimum distance.
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Q3. 
Rotting Oranges Problem Statement
You are given a grid containing oranges where each cell of the grid can contain one of the three integer values:
• 0 - representing an empty cell
• 1 - representing a fre...read more
Ans. 
Find the minimum time required to rot all fresh oranges in a grid.
• Use Breadth First Search (BFS) to simulate the rotting process of oranges.

• Track the time taken to rot all fresh oranges and return the result.

• If any fresh oranges remain after simulation, return -1 as it is impossible to rot all oranges.
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Round duration - 45 minutes
Round difficulty - Medium

Timing: 2:00 pm
Online round over google meet, code at google docs.
The interviewer was friendly, encouraging, and humble.

Q1. 
Smallest Integer Not Representable as Subset Sum
Given a non-decreasing sorted array ARR of N positive numbers, determine the smallest positive integer that cannot be expressed as the sum of elements from...read more
Ans. 
The task is to find the smallest positive integer value that cannot be represented as a sum of elements of any proper subset of the given array.
• The array is sorted in non-decreasing order, so we can iterate through the array and keep track of the maximum sum we can form.

• If the current element is greater than the maximum sum + 1, then the maximum sum + 1 is the smallest positive integer that cannot be represented.

• If all...read more
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Round duration - 45 minutes
Round difficulty - Medium

Timing: 2:00 pm
Online round over google meet, code at google docs.
The interviewer was not speaking much. It was a bit strange.

Q1. 
Bottom Right View of Binary Tree Problem Statement
Your task is to identify and return the bottom right view of a given binary tree.
This involves viewing the binary tree from an angle of 45 degrees from...read more
Ans. 
Identify and return the bottom right view of a given binary tree by viewing it from an angle of 45 degrees from the bottom right side.
• Traverse the binary tree in a right-to-left manner and keep track of the last node encountered at each level.

• Use a queue for level order traversal and update the result array with the last node at each level.

• Return the result array sorted in ascending order as the bottom right view of th
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Round duration - 30 Minutes
Round difficulty - Easy

Timing: 7:00 pm
The interviewer was friendly and in a bit of a hurry.