Paytm Full Stack Developer Interview Questions, Process, and Tips

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. DFS
1. Create two variables, one for storing the sum of nodes at the odd level and one for storing the sum of nodes at even level.
2. Use the below algorithm to calculate level sums where:
oddSum: denotes sum of nodes at odd levels, initially 0.
evenSum: denotes sum of nodes at ecen levels, initially 0.
level: the level of the current node, initially 1. 
void oddEvenLevelHelper(current, oddSum, evenSum, level)
 
• If the cur...read more
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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. Naïve Solution
The idea is very simple and naive. We will process the rotten oranges second by second. Each second, we rot all the fresh oranges that are adjacent to the already rotten oranges. The time by which there are no rotten oranges left to process will be our minimum time.
 
In the first traversal of the grid, we will process all the cells with value 2 (rotten oranges). We will also mark their adjacent cells ...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. Optimal Approach
Initialize a variable ‘direction’ with 0 which means that the robot is initially facing towards the north.
direction: 0 -> Robot is facing towards the North
direction: 1 -> Robot is facing towards the West 
direction: 2 -> Robot is facing towards the South 
direction: 3 -> Robot is facing towards the West
 
Initialize two variables ‘x’ and ‘y’ as 0. They will represent the position ...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. Transpose and Reverse
The idea is to find the transpose of the given matrix and then reverse the columns of the transposed matrix. For example:
For the given 2D matrix:
	[ [ 1,  2,  3 ],
	  [ 4,  5,  6 ],
	  [ 7,  8,  9 ] ]
After taking transpose, it will become:
	[ [ 1,  4,  7 ],
	  [ 2,  5,  8 ],
	  [ 3,  6,  9 ] ]
After reversing the columns, it will ...read more
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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. Brute Force
• The idea is pretty simple, as we can add only at the front, thus, we need to work on the prefix of the string.
• We need to find the largest prefix that is a palindrome. For example, in case of “abbac”, the largest prefix that is a palindrome is “abba”, now all you need to do is add the reverse of left out suffix i.e. “ca” at the front to make it a palindrome.
• This can be done in the following way:-
  • Until the str...read more
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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. Using while() loop
• This can be done using an if-else-if ladder to check for negative,0, and positive numbers.
• If the input is a positive number use a while loop to multiply n with n-1, n-2…1 and get the desired output.
Space Complexity: O(1)Explanation: Time Complexity: O(1)Explanation:
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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. Brute Force
For every element in the array, we will run a loop on its right side. As soon as we find an element on its right side which is greater than it, we will break the loop, assign it as the NGE of this element, move forward, and do the same for the next element.
Space Complexity: O(1)Explanation:
O(1)
 
No extra space is used.
Time Complexity: O(n^2)Explanation:
O(N ^ 2),  Where N is the number of elements ...read more
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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. Brute Force
We will traverse the Binary search tree from the root node till we find the node whose key value is given, and upon getting that, we return the ceil value of it.

 
The steps are as follows:  
• Initialize ‘ceilValue’ to store the ceil value to be returned.
• We run a while loop till the value of the node is not equal to NULL.
  • If the value of the node is equal to ‘X’’ then we return the node value.
  • If th...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. Brute Force
In this approach, we consider every possible subarray that can be formed from the given array ‘ARR’. For every subarray ARR[i … j] considered, we need to check whether this is the smallest unsorted subarray or not.
 
The algorithm is as follows:
1. Let’s take the variable ‘ANS’ equal to 'N' (the length of the array) initially.
2. Now for every subarray ARR[i … j], we will find the maximum and minimum value lying ...read more
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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. Sorting
Use any good sorting algorithm like Merge Sort, Quick Sort or inbuilt sorting function of different languages.
• Sort the Array and just return.
Space Complexity: O(1)Explanation:
O(1), As we are using constant space.
Time Complexity: O(nlogn)Explanation:
O(N*log(N)), where ‘N’ is the size of the array.
We are using inbuilt sort algorithm which has Overall Time Complexity O(N*log(N))
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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. Recursive Solution
• Find the levels of both the given nodes.
• This can be done by making a separate function for finding the level/by using level order traversal.
• The levels should be the same.
• Check if both the nodes are siblings or not.
• This can again be done by simply going through the entire Binary Tree and checking if the node’s children are the given two nodes. If this is true, then given two nodes are siblings and henc...read more
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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?
Ans. 
Tip 1 : Do prepare such questions before hand only.
Tip 2 : Speak confidently.
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Q2. How was your experience with the previous two technical rounds?
Ans. 
Tip 1 : Do remember the names of the interviewers who took your interview.
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Q3. What do you know about Paytm?
Ans. 
Tip 1 : Do a research before hand about what does the company do.
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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. Brute Force
The brute force approach to find all the bridges in a given graph is to check for every edge if it is a bridge or not, by first not considering current edge is not in given graph and then checking if the vertices that it was connecting are still connected or not, using DFS(DepthFirst Search). Given below is an algorithm that will find all bridges in a graph.
 
Algorithm :
1. Initialise a visited array with fa...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
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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
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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
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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
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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
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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
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Q3. What is a nested SQL query?
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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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