Paytm Software Developer Interview Questions, Process, and Tips

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
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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
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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
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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
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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 - 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. 
I used a recursive approach to solve the problem.
Let's say we have a string S[L.......H].
Then our solution can be found as-
if(S[L]==S[H])
minInsertion(S[L+1....H-1]
else (minInsertion(S[L....H-1]), minInsertion(S[L+1....H])+1)
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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. 
I used a simple traverse approach to solve the question.
The idea was to first traverse the subtree rooted with give node and find the closest leaf in this subtree. Store this distance. Now traverse tree starting from root. If given node x is in left subtree of root, then find the closest leaf in right subtree, else find the closest left in left subtree.
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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. 
I used an optimized approach to solve it.
1. Reverse Both Lists
2. Now traverse both lists and add numbers
3. Reverse resultant linked list and return head
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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. 
It is quite an easy problem if you know about arrays.
1. Firstly I sorted the array
2. Then I took 2 pointers.
3. I iterated one from start and other from end and checked sum at each step.
4. I returned the value of element if sum equals K else continue until start<= last
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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. 
I explained the algorithm of Quick Sort and wrote its code in C++.He also asked me to explain its time complexity.
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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. 
I explained the algorithm of Merge Sort and wrote its code in C++.He also asked me to explain its time complexity.
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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. 
1) Create an empty stack S.
2) Initialize current node as root
3) Push the current node to S and set current = current->left until current is NULL
4) If current is NULL and stack is not empty then
a) Pop the top item from stack.
b) Print the popped item, set current = popped_item->right
c) Go to step 3.
5) If current is NULL and stack is empty then we are done.

 
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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. 
1. Zigzag traversal can be implemented using two stacks.
2. Keep track of the direction to traverse using the bool variable isLtoR. If isLtoR is true, then the current level needs to be traversed from left to right and vice versa.
3. Push the root node into curr and set isLtoR to false for the next level.
4. Pop a node from curr and store it in the variable temp. Deduce the direction from isLtoR and decide, depending on t...read more
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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.