Practo Software Developer Interview Questions, Process, and Tips

Coding test based on Binary trees, String Manipulation

Round duration - 90 minutes
Round difficulty - Medium

This round had 3 coding questions of Medium to Hard level of difficulty.

Q1. 
Intersection of Two Unsorted Arrays Problem Statement
Given two integer arrays ARR1 and ARR2 of sizes 'N' and 'M' respectively, find the intersection of these arrays. The intersection is defined as the se...read more
Ans. 
Approach 1 (Using Hashing) :

1) Initialize an empty set hs.
2) Iterate through the first array and put every element of the first array in the set S.
3) For every element x of the second array, do the following :
Search x in the set hs. If x is present, then print it.


TC : O(N+M) under the assumption that hash table search and insert operations take O(1) time, here N=size of array
1 and M=size of array 2.
SC : O(min(N,M))



Appr...read more
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Q2. 
Ways To Make Coin Change
Given an infinite supply of coins of varying denominations, determine the total number of ways to make change for a specified value using these coins. If it's not possible to make...read more
Ans. 
This was a very standard DP problem and I had already solved it on platforms like LeetCode and CodeStudio so I
was able to come up with the logic and code it preety fast.


Steps :

1) Create a two-dimensional array, ‘dp’, where ‘dp[i][j]’ will denote the total number of ways to make j value by using i
coins.

2) Run 2 loops ,1st one from 1 to value and second one throught the array denominations.

3) Fill dp array by the recurre...read more
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Q3. 
Longest Substring Without Repeating Characters Problem Statement
Given a string S of length L, determine the length of the longest substring that contains no repeating characters.
Example:
Input:
"abac...read more
Ans. 
Approach : I solved it using 2-pointers and keeping a track of the frequency of the elements encountered in a freq
array of size 26.

Steps :

1) Initiliase a freq array of size 26 where a=0, b=1 ...,z=25 .
2) Let s be our string and n = s.size()
3) Do , freq[s[0]]++;
4) Keep 2 pointers start and end where initially start=0 and end=1 also maintain a answer variable ans where initially
ans=0
5) Now run a loop till end=1 and start...read more
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Round duration - 60 minutes
Round difficulty - Medium

This round started with 2 coding questions and then moved on to some more questions from OOPS.

Q1. 
Palindrome Linked List Problem Statement
You are provided with a singly linked list of integers. Your task is to determine whether the given singly linked list is a palindrome. Return true if it is a pali...read more
Ans. 
Approach :

1) Recursively traverse the entire linked list to get the last node as a rightmost node.

2) When we return from the last recursion stack. We will be at the last node of the Linked List. Then the last node
value is compared with the first node value of Linked List.

3) In order to access the first node of Linked List, we create a global left pointer that points to the head of Linked List
initially that will be avai...read more
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Q2. 
Search Element in a Rotated Sorted Array
Given a sorted array that has been rotated, the task is to find the index of a specific element. The array is initially sorted in ascending order and then rotated ...read more
Ans. 
This was a preety standard Binary Search Question and I had solved this question before on platforms like LeetCode
and CodeStudio . I was asked this question to test my implementation skills and how well do I handle Edge Cases .

Approach :

1) The idea is to find the pivot point, divide the array in two sub-arrays and perform binary search.

2) The main idea for finding pivot is – for a sorted (in increasing order) and pivot...read more
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Q3. What is a static variable in C?
Ans. 
1) Static variables are initialized only once.
2) The compiler persists with the variable till the end of the program.
3) Static variables can be defined inside or outside the function.
4) They are local to the block.
5) The default value of static variables is zero.
6) The static variables are alive till the execution of the program.

Here is the syntax of static variables in C language,

static datatype variable_name = value;

...read more
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Q4. What is the difference between abstraction and inheritance?
Ans. 
The main difference between abstraction and inheritance is that abstraction allows hiding the internal details and displaying only the functionality to the users, while inheritance allows using properties and methods of an already existing class.
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Round duration - 60 minutes
Round difficulty - Medium

This round had questions mainly from HTML,CSS and JavaScript as I had mentioned some Frontend Projects in my resume so the interviewer wanted to check my skills on those. He also asked me some SQL queries and a simple coding question towards the end of the interview.

Q1. What is event bubbling in JavaScript?
Ans. 
Event bubbling is a method of event propagation in the HTML DOM API when an event is in an element inside another element, and both elements have registered a handle to that event. It is a process that starts with the element that triggered the event and then bubbles up to the containing elements in the hierarchy. In event bubbling, the event is first captured and handled by the innermost element and then propagated to...read more
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Q2. How can you optimize the loading of website assets?
Ans. 
To optimize website load time we need to optimize its asset loading and for that:

1) CDN hosting - A CDN or content delivery network is geographically distributed servers to help reduce latency.

2) File compression - This is a method that helps to reduce the size of an asset to reduce the data transfer

3) File concatenation - This reduces the number of HTTP calls

4) Minify scripts - This reduces the overall file size of js...read more
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Q3. In how many ways can you display HTML elements?
Ans. 
1) inline: Using this we can display any block-level element as an inline element. The height and width attribute values of the element will not affect.

2) block: using this, we can display any inline element as a block-level element. 

3) inline-block: This property is similar to inline, except by using the display as inline-block, we can actually format the element using height and width values.

4) flex: It displays...read more
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Q4. 
Check if Two Strings are Anagrams
Anagrams are words or names that can be formed by rearranging the letters of another word. For instance, 'spar' can be rearranged to form 'rasp', making them anagrams.
E...read more
Ans. 
Approach 1(Using Sorting) : 
1) Sort both strings
2) Compare the sorted strings

TC : O(N*log(N)), where N = length of the string
SC : O(1)


Approach 2(Counting characters) : 

1) Create count arrays of size 256 for both strings. Initialize all values in count arrays as 0.
2) Iterate through every character of both strings and increment the count of character in the corresponding count arrays.
3) Compare count arrays. I...read more
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Round duration - 30 minutes
Round difficulty - Easy

This is a cultural fitment testing round. HR was very frank and asked standard questions. Then we discussed about my role.

Q1. What is something about you that is not included in your resume?
Ans. 
If you get this question, it's an opportunity to choose the most compelling information to share that is not obvious from your resume.

Example :

Strength -> I believe that my greatest strength is the ability to solve problems quickly and efficiently, which makes me unique from others.

Ability to handle Pressure -> I enjoy working under pressure because I believe it helps me grow and become more efficient.

Tip : Empha...read more
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Q2. Why should we hire you?
Ans. 
Tip 1 : The cross questioning can go intense some time, think before you speak.

Tip 2 : Be open minded and answer whatever you are thinking, in these rounds I feel it is important to have opinion.

Tip 3 : Context of questions can be switched, pay attention to the details. It is okay to ask questions in these round, like what are the projects currently the company is investing, which team you are mentoring. How all is the...read more
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Round duration - 90 minutes
Round difficulty - Medium

This round had 3 coding questions of Medium to Hard level of difficulty.

Q1. 
Balanced Parentheses Combinations
Given an integer N representing the number of pairs of parentheses, find all the possible combinations of balanced parentheses using the given number of pairs.
Explanati...read more
Ans. 
Approach :
1) First make a recursive function, say ‘solve’ taking the number of opening brackets ‘opening’, number of closing
brackets ‘closing’ output string ‘output’, and an array of strings ‘ans’ as arguments.

2) Make the base condition as if ‘opening’ = 0 and ‘closing’ = 0 then push the output string in the ‘ans’ and return.

3) If ‘opening’ is not equal to zero then call the ‘solve’ function recursively by decrementing...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
Ans. 
Approach 1 (Brute Force) :

1) Iterate over every elevation or element and find the maximum elevation on to the left and right of it. Say, the
maximum elevation on to the left of the current elevation or element that we are looking at is ‘maxLeftHeight’ and the
maximum elevation on to the right of it is ‘maxRightHeight’.

2) Take the minimum of ‘maxLeftHeight’ and ‘maxRightHeight’ and subtract it from the current elevation o...read more
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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. 
Approach : I solved this problem using Multisource-BFS as I had solved questions similar to this while preparing for
my interviews.

Steps :

1) Initialize ‘TIME’ to 0.

2) Declare a Queue data structure and a 2D boolean array ‘VISITED’.

3) Push all cells with rotten orange to the queue.

4) Loop till queue is not empty
4.1) Get the size of the current level/queue.
4.2) Loop till the 'LEVEL_SIZE' is zero:
i) Get the front cell of t...read more
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Round duration - 60 Minutes
Round difficulty - Medium

This was a standard DS/Algo round where I was given 2 questions to solve under 60 minutes. I was able to come up with the optimal approach for both the questions and then at the end of the interview I was also asked the famous Die Hard Water Puzzle.

Q1. 
Queue Using Stacks Implementation
Design a queue data structure following the FIFO (First In First Out) principle using only stack instances.
Explanation:
Your task is to complete predefined functions t...read more
Ans. 
A queue can be implemented using two stacks. Let queue to be implemented be q and stacks used to implement q be stack1 and stack2. q can be implemented in two ways: 

Approach 1 (By making enQueue operation costly) : This method makes sure that oldest entered element is always at the top of stack 1, so that deQueue operation just pops from stack1. To put the element at top of stack1, stack2 is used. 

enQueue(q, ...read more
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Q2. 
Merge Intervals Problem Statement
You are provided with 'N' intervals, each containing two integers denoting the start time and end time of the interval.
Your task is to merge all overlapping intervals a...read more
Ans. 
Approach :

1) We will first sort the intervals by non-decreasing order of their start time.

2) Then we will add the first interval to our resultant list.

3) Now, for each of the next intervals, we will check whether the current interval is overlapping with the last interval in
our resultant list.

4) If it is overlapping then we will update the finish time of the last interval in the list by the maximum of the finish time
of ...read more
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Q3. You have a 3-liter jar and a 5-liter jar. How can you measure exactly 4 liters using these two jars?
Ans. 
Approach : 

1) Fill the 5 liter jug from the tap.
2) Empty the 5 liter jug into the 3 liter jug - leaving 2 liters in the 5 liter jug.
3) Pour away the contents of the 3 liter jug.
4) Fill the 3 liter jug with the 2 liters from the 5 liter jug - leaving 2 liters in the 3 liter jug.
5) Fill the 5 liter jug from the tap.
6) Fill the remaining 1 liter space in the 3 liter jug from the 5 liter jug.
7) Leaving 4 liters in the
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Round duration - 60 Minutes
Round difficulty - Medium

This round had 2 coding questions - first one related to Binary Tree and the second one was a simple question from Bit Manipulation. This was followed by some questions from OOPS.

Q1. 
Binary Tree Diameter Problem Statement
You are given a Binary Tree, and you need to determine the length of the diameter of the tree.
The diameter of a binary tree is the length of the longest path betwe...read more
Ans. 
Approach 1 :

Steps :

1) If the ‘root’ node is NULL, return 0. The diameter of an empty tree is 0.
2) Recur for the left subtree and store the diameter of the left subtree in a variable ‘leftDiameter’, i.e.
‘leftDiameter’ = getDiameter(left child of the root node)
3) Similarly, recur for the right subtree and store the diameter of the right subtree in a variable
‘rightDiameter’ i.e. ‘rightDiameter’ = getDiameter(right child o...read more
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Q2. 
Power of 2 Problem Statement
Determine if it is possible to reorder the digits of a given integer 'N' such that the resulting number is a power of two. The leading digit must not be zero.
Input:
The fir...read more
Ans. 
Approach : If a number N is power of 2 then bitwise & of N and N-1 will be zero. We can say N is a power of 2 or not
based on the value of N&(N-1). The expression N&(N-1) will not work when N is 0.
So,handle that case separately.

TC : O(1)
SC : O(1)
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Q3. What are some advantages of using Object-Oriented Programming (OOP)?
Ans. 
1) OOPs is very helpful in solving very complex level of problems.
2) Highly complex programs can be created, handled, and maintained easily using object-oriented programming.
3) OOPs, promote code reuse, thereby reducing redundancy.
4) OOPs also helps to hide the unnecessary details with the help of Data Abstraction.
5) OOPs, are based on a bottom-up approach, unlike the Structural programming paradigm, which uses a top-d...read more
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Q4. What are access specifiers and what is their significance in Object-Oriented Programming?
Ans. 
Access specifiers, as the name suggests, are a special type of keywords, which are used to control or specify the
accessibility of entities like classes, methods, etc. Some of the access specifiers or access modifiers include “private”,
“public”, etc. These access specifiers also play a very vital role in achieving Encapsulation - one of the major features
of OOPs.
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Round duration - 30 Minutes
Round difficulty - Easy

This was my last round and I hoped it to go good just like the other rounds. The interviewer was very straight to point
and professional. The interview lasted for 30 minutes.

Q1. Why should we hire you?
Ans. 
Tip 1 : The cross questioning can go intense some time, think before you speak.

Tip 2 : Be open minded and answer whatever you are thinking, in these rounds I feel it is important to have opinion.

Tip 3 : Context of questions can be switched, pay attention to the details. It is okay to ask questions in these round,
like what are the projects currently the company is investing, which team you are mentoring. How all is the ...read more
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