Paytm Full Stack Developer Interview Questions and Answers

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...read more
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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...read more
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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 - 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...read more
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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...read more
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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 ...read more
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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 ...read more
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Round duration - 90 minutes
Round difficulty - Medium

It was in the evening, at around 3 - 4 PM. There were 3 coding questions. One easy, two moderate ones. The platform had autocomplete feature too.

Q1. 
Problem Statement: Parity Move
You have an array of integers, and your task is to modify the array by moving all even numbers to the beginning while placing all odd numbers at the end. The order within ev...read more
Ans. 
Move all even numbers to the beginning and odd numbers to the end of an array.
• Iterate through the array and swap even numbers to the front and odd numbers to the back.

• Use two pointers, one starting from the beginning and one from the end, to achieve the desired arrangement.

• Return the modified array with even numbers at the start and odd numbers at the end.
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Q2. 
Anagram Pairs Verification Problem
Your task is to determine if two given strings are anagrams of each other. Two strings are considered anagrams if you can rearrange the letters of one string to form the...read more
Ans. 
Determine if two strings are anagrams of each other by checking if they have the same characters in different order.
• Create a character frequency map for both strings and compare them.

• Sort both strings and compare if they are equal.

• Use a hash table to store character counts and check if they are the same for both strings.
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Q3. 
LCA in a Binary Search Tree
You are given a binary search tree (BST) containing N nodes. Additionally, you have references to two nodes, P and Q, within this BST.
Your task is to determine the Lowest Com...read more
Ans. 
Find the Lowest Common Ancestor (LCA) of two nodes in a Binary Search Tree (BST).
• Traverse the BST from the root node to find the LCA of the given nodes.

• Compare the values of the nodes with the values of P and Q to determine the LCA.

• If the values of P and Q are on opposite sides of the current node, then the current node is the LCA.
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Round duration - 50 Minutes
Round difficulty - Medium

They asked 2 coding questions and 2 sql queries in this round

Q1. 
Find the Longest Palindromic Substring
Given a string ‘S’ composed of lowercase English letters, your task is to identify the longest palindromic substring within ‘S’.
If there are multiple longest palin...read more
Ans. 
Find the longest palindromic substring in a given string, returning the rightmost one if multiple exist.
• Iterate through each character in the string and expand around it to find palindromes

• Keep track of the longest palindrome found and its starting index

• Return the substring starting from the index of the longest palindrome found
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Q2. 
Trapping Rain Water Problem Statement
You are given a long type array/list ARR of size N, representing an elevation map. The value ARR[i] denotes the elevation of the ith bar. Your task is to determine th...read more
Ans. 
Calculate the total amount of rainwater that can be trapped between given elevations in an array.
• Iterate through the array and calculate the maximum height on the left and right of each bar.

• Calculate the amount of water that can be trapped at each bar by taking the minimum of the maximum heights on the left and right.

• Sum up the trapped water at each bar to get the total trapped water for the entire array.
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Q3. What is a nested SQL query?
Ans. 
A nested SQL query is a query within another query, used to retrieve data from multiple tables in a single query.
• Nested queries are enclosed within parentheses and can be used in SELECT, INSERT, UPDATE, or DELETE statements.

• They are commonly used to perform subqueries to filter results based on the output of the inner query.

• Example: SELECT * FROM table1 WHERE column1 IN (SELECT column2 FROM table2 WHERE condition);
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Round duration - 50 Minutes
Round difficulty - Medium

This round was about OS, networking and my projects. What are the different ways to style a React component?
Name a few techniques to optimize React app performance.

Round duration - 30 Minutes
Round difficulty - Easy

It was a fun round, in which they ask about your preferences about programming languages, technologies or your hobbies. If you reach this round, it means that your chances of selection are 99%.

Q1. What was the biggest hurdle you faced while developing a project?
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