Paytm Full Stack Developer Interview Questions, Process, and Tips

Round duration - 70 minutes
Round difficulty - Medium

The test started around 3 pm and was of 70 minutes. 3 coding questions were asked which were mainly on trees and number theory.

Q1. 
Factorial Calculation Problem Statement
Develop a program to compute the factorial of a given integer 'n'.
The factorial of a non-negative integer 'n', denoted as n!, is the product of all positive integ...read more
Ans. 
Program to compute factorial of a given integer 'n', with error handling for negative values.
• Create a function to calculate factorial using a loop or recursion

• Check if input is negative, return 'Error' if true

• Handle edge cases like 0 and 1 separately

• Return the calculated factorial value
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Q2. 
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. 
The task is to find the Next Greater Element for each element in a list of integers.
• Iterate through the list of integers from right to left

• Use a stack to keep track of elements whose NGE is yet to be found

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

• Assign the NGE as the top element of the stack or -1 if the stack is empty
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Q3. 
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 the smallest integer greater than or equal to the given number.
• Traverse the BST to find the closest integer greater than or equal to the given key.

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

• Recursively traverse left or right subtree based on the key value to find the ceil value.

• Return the ceil value once found for each test case
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Round duration - 60 minutes
Round difficulty - Medium

Interviewer was very friendly and supportive. My interview happened on google meet. What is a View? What is Denormalization? Difference between “==” and “===” operators in js.

Q1. 
Sub Sort Problem Statement
You are given an integer array ARR. Determine the length of the shortest contiguous subarray which, when sorted in ascending order, results in the entire array being sorted in a...read more
Ans. 
Determine the length of the shortest contiguous subarray that needs to be sorted to make the entire array sorted in ascending order.
• Iterate from left to right to find the first element out of order.

• Iterate from right to left to find the last element out of order.

• Calculate the length of the subarray between the two out of order elements.
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Q2. 
Sort 0 1 2 Problem Statement
Given an integer array arr of size 'N' containing only 0s, 1s, and 2s, write an algorithm to sort the array.
Input:
The first line contains an integer 'T' representing the n...read more
Ans. 
Sort an integer array containing only 0s, 1s, and 2s in linear time complexity.
• Use three pointers to keep track of 0s, 1s, and 2s while traversing the array.

• Swap elements based on the values encountered to sort the array in-place.

• Time complexity should be O(N) to solve the problem efficiently.
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Round duration - 60 minutes
Round difficulty - Medium

What are some of the advantages of Angular over other frameworks?

Q1. 
Cousin Nodes in a Binary Tree
Determine if two nodes in a binary tree are cousins. Nodes are considered cousins if they are at the same level and have different parents.
Explanation:
In a binary tree, e...read more
Ans. 
Determine if two nodes in a binary tree are cousins based on level and parent nodes.
• Traverse the binary tree to find the levels and parents of the given nodes.

• Check if the nodes are at the same level and have different parents to determine if they are cousins.

• Return 'YES' if the nodes are cousins, 'NO' otherwise.

• Example: For input '1 2 3 4 -1 5 6 -1 7 -1 -1 -1 -1 -1 -1' and nodes 4 7, output is 'YES'.
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Round duration - 10 minutes
Round difficulty - Easy

I got a call from HR in the evening around 6:30 pm.

Q1. Can you tell me about yourself?
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Q2. How was your experience with the previous two technical rounds?
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Q3. What do you know about Paytm?
Ans. 
Paytm is a leading Indian digital payment platform offering a wide range of services including mobile recharges, bill payments, and online shopping.
• Founded in 2010 by Vijay Shekhar Sharma

• Offers services like mobile recharges, bill payments, online shopping, and digital wallet

• Acquired by One97 Communications in 2013

• Expanded into financial services like Paytm Payments Bank and Paytm Money

• One of the largest digital paymen
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Round duration - 70 minutes
Round difficulty - Medium

There were 3 problems 1 was easy and 2 were of medium types.

Q1. 
Odd Even Levels in Binary Tree
Given a binary tree, the task is to compute the modulus of the difference between the sum of nodes at odd levels and the sum of nodes at even levels.
Input:
The first line...read more
Ans. 
The task is to compute the modulus of the difference between the sum of nodes at odd levels and the sum of nodes at even levels in a binary tree.
• Traverse the binary tree level by level and calculate the sum of nodes at odd and even levels separately.

• Find the absolute difference between the sums and return the modulus of this difference.

• Handle null nodes by skipping them during the sum calculation.
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Q2. 
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.
• Create a queue to store the rotten oranges and their time of rotting.

• Iterate through the grid to find all rotten oranges and add them to the queue.

• Simulate the rotting process by checking adjacent cells and updating their status.

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

• Handle edge cases like unreachable fresh oranges or already
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Round duration - 50 minutes
Round difficulty - Medium

the interviewer was very polite and straightforward, he didn't ask me to introduce myself and he directly jumps to the coding problems.
What is new about the relationship between the and tags in HTML5?
Explain Components, Modules and Services in Angular

Q1. 
Circular Move Problem Statement
You have a robot currently positioned at the origin (0, 0) on a two-dimensional grid, facing the north direction. You are given a sequence of moves in the form of a string ...read more
Ans. 
Determine if a robot's movement path is circular on a 2D grid given a sequence of moves.
• Iterate through the move sequence and update the robot's position based on the moves ('L' - turn left, 'R' - turn right, 'G' - move forward).

• Check if the robot returns to the starting position after completing the move sequence.

• If the robot ends up at the starting position and facing the north direction, the movement path is circula
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Round duration - 70 minutes
Round difficulty - Easy

What is a View in sql? What are the TRUNCATE, DELETE and DROP statements?

Q1. 
Rotate Matrix by 90 Degrees Problem Statement
Given a square matrix 'MATRIX' of non-negative integers, rotate the matrix by 90 degrees in an anti-clockwise direction using only constant extra space.
Inpu...read more
Ans. 
Rotate a square matrix by 90 degrees in an anti-clockwise direction using constant extra space.
• Iterate through each layer of the matrix from outer to inner layers

• Swap elements in groups of 4 to rotate the matrix

• Handle odd-sized matrices by adjusting the center element if needed
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Q2. 
Minimum Characters to Make a String Palindrome
Given a string STR of length N, determine the minimum number of characters to be added to the front of the string to make it a palindrome.
Input:
The first...read more
Ans. 
The task is to find the minimum number of characters needed to be added to the front of a string to make it a palindrome.
• Iterate through the string from both ends and count the number of characters that need to be added to make it a palindrome.

• Use two pointers approach to compare characters from start and end of the string.

• Keep track of the count of characters needed to be added to form a palindrome.
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Round duration - 20 minutes
Round difficulty - Easy

Round duration - 70 minutes
Round difficulty - Easy

there was some coding questions and some mcqs related to js, html, css, java and aptitude.

Q1. 
Bridge in Graph Problem Statement
Given an undirected graph with V vertices and E edges, your task is to find all the bridges in this graph. A bridge is an edge that, when removed, increases the number of...read more
Ans. 
Find all the bridges in an undirected graph by identifying edges that, when removed, increase the number of connected components.
• Use Tarjan's algorithm to find bridges in the graph.

• Keep track of the discovery time and low time of each vertex during DFS traversal.

• An edge (u, v) is a bridge if low[v] > disc[u].

• Handle multiple test cases efficiently to find bridges in each graph.

• Ensure the output contains the count of
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Q2. 
House Robber Problem Statement
Mr. X is a professional robber with a plan to rob houses arranged in a circular street. Each house has a certain amount of money hidden, separated by a security system that ...read more
Ans. 
The task is to find the maximum amount of money Mr. X can rob from houses arranged in a circle without alerting the police.
• The problem can be solved using dynamic programming.

• Create two arrays to store the maximum amount of money robbed when considering the first house and when not considering the first house.

• Iterate through the array and update the maximum amount of money robbed at each house.

• The final answer will be
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Round duration - 90 Minutes
Round difficulty - Easy

MCQ based on web and oops.

Q1. 
Subtree of Another Tree Problem Statement
Given two binary trees, T and S, determine whether S is a subtree of T. The tree S should have the same structure and node values as a subtree of T.
Explanation:
...read more
Ans. 
Determine if one binary tree is a subtree of another binary tree based on their structure and node values.
• Traverse through the main tree and check if any subtree matches the second tree

• Use recursion to compare nodes of both trees

• Handle edge cases like empty trees or null nodes

• Check if the root node of the second tree exists in the main tree
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Round duration - 50 Minutes
Round difficulty - Easy

This round involved a discussion of a project I had undertaken recently and a coding problem. How does an Angular application work? List out differences between AngularJS and Angular

Q1. 
Count Ways to Reach the N-th Stair Problem Statement
You are provided with a number of stairs, and initially, you are located at the 0th stair. You need to reach the Nth stair, and you can climb one or tw...read more
Ans. 
The task is to find the number of distinct ways to climb from the 0th step to the Nth step, where each time you can climb either one step or two steps.
• Use dynamic programming to solve this problem

• Create an array to store the number of ways to reach each step

• Initialize the first two elements of the array as 1 and 2

• For each subsequent step, the number of ways to reach that step is the sum of the number of ways to reach t...read more
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Round duration - 80 Minutes
Round difficulty - Medium

The interview mostly focused on coding problems and Java-related concepts.

Q1. How is a Linked List implemented in Java, and when would you prefer it over an ArrayList?
Ans. 
A Linked List in Java is implemented using nodes with references to the next node. It is preferred over an ArrayList when frequent insertions and deletions are required.
• In Java, a Linked List is implemented using a Node class with data and a reference to the next Node.

• LinkedList class in Java provides methods like add(), remove(), and get() for manipulating the list.

• Linked List is preferred over ArrayList when frequent...read more
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Q2. 
Prerequisite Task Completion Verification
Given a positive integer 'N', representing the number of tasks, and a list of dependency pairs, determine if it is possible to complete all tasks considering thes...read more
Ans. 
Determine if it is possible to complete all tasks considering prerequisites.
• Create a graph representation of the tasks and dependencies.

• Use topological sorting to check if there is a cycle in the graph.

• Return 'Yes' if no cycle is found, 'No' otherwise.
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Q3. 
Kth Smallest and Largest Element Problem Statement
You are provided with an array 'Arr' containing 'N' distinct integers and a positive integer 'K'. Your task is to find the Kth smallest and Kth largest e...read more
Ans. 
Find the Kth smallest and largest elements in an array.
• Sort the array to easily find the Kth smallest and largest elements.

• Ensure K is within the array's size to avoid errors.

• Handle multiple test cases efficiently.

• Consider edge cases like when N is small or K is at the extremes.
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Round duration - 30 Minutes
Round difficulty - Easy

This was the Hiring Manager Round. What is a Primary Key? What is a Cross-Join? What is the difference between Clustered and Non-clustered index?

Q1. 
Search in a Row-wise and Column-wise Sorted Matrix Problem Statement
You are given an N * N matrix of integers where each row and each column is sorted in increasing order. Your task is to find the positi...read more
Ans. 
Given a sorted N * N matrix, find the position of a target integer 'X'.
• Iterate over rows and columns to search for the target integer 'X'.

• Utilize the sorted nature of the matrix to optimize the search process.

• Return the position of 'X' if found, else return '-1 -1'.
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