Practo Interview Questions, Process, and Tips

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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