30+ Practo Software Developer Interview Questions and Answers

Find the intersection of two unsorted arrays while maintaining the order of elements from the first array.

• Iterate through the elements of the first array and check if they exist in the second array.

• Use a hash set to keep track of elements already seen in the second array for efficient lookup.

• Maintain the order of elements from the first array while finding the intersection.

• Handle duplicate elements in both arrays appropriately.

• Output the intersection elements in the order the...read more

Find the minimum time required to rot all fresh oranges adjacent to rotten oranges.

• Create a queue to store the coordinates of rotten oranges and perform BFS to rot adjacent fresh oranges.

• Track the time taken to rot all fresh oranges and return -1 if not all fresh oranges can be rotten.

• Update the grid with the new state of oranges after each second.

• Handle edge cases such as empty grid or no fresh oranges present.

• Example: For the given grid, the minimum time required is 4 secon...read more

The problem involves determining if it is possible to reorder the digits of a given integer to form a power of 2.

• Iterate through all possible permutations of the digits of the given integer.

• Check if any of the permutations form a power of 2.

• Return 1 if a valid permutation is found, else return 0.

Check if a given singly linked list is a palindrome or not.

• Traverse the linked list to find the middle element using slow and fast pointers.

• Reverse the second half of the linked list.

• Compare the first half with the reversed second half to determine if it's a palindrome.

The task is to determine the total number of ways to make change for a specified value using given denominations.

• Create a function that takes in the number of denominations, the denominations array, and the value to make change for as input

• Use dynamic programming to iterate through all possible combinations of coins to make the specified value

• Keep track of the number of ways to make change for each value from 0 to the target value

• Return the total number of ways to make change...read more

The task is to find the diameter of a binary tree, which is the length of the longest path between any two end nodes in the tree.

• Traverse the tree to find the longest path between two nodes.

• Keep track of the maximum diameter found during traversal.

• The diameter may not necessarily pass through the root node.

• Consider both left and right subtrees while calculating the diameter.

• Example: For input 1 2 3 4 -1 5 6 -1 7 -1 -1 -1 -1 -1 -1, the diameter is 6.

Generate all possible combinations of balanced parentheses for a given number of pairs.

• Use recursion to generate all possible combinations of balanced parentheses.

• Keep track of the number of open and close parentheses used in each combination.

• Return the valid combinations as an array of strings.

Implement a queue using stacks following FIFO principle.

• Use two stacks to simulate a queue.

• For enQueue operation, push elements onto stack1.

• For deQueue operation, if stack2 is empty, pop all elements from stack1 and push onto stack2, then pop from stack2.

• For peek operation, if stack2 is empty, pop all elements from stack1 and push onto stack2, then return top of stack2.

• For isEmpty operation, check if both stack1 and stack2 are empty.

• Example: enQueue(5), enQueue(10), peek(), d...read more

Merge overlapping intervals and return sorted list of merged intervals by start time.

• Sort the intervals based on start time.

• Iterate through intervals and merge overlapping ones.

• Return the merged intervals in sorted order.

Search for an element in a rotated sorted array efficiently in O(logN) time complexity.

• Implement binary search to find the pivot point where rotation occurs.

• Divide the array into two subarrays and perform binary search on the appropriate subarray.

• Handle cases where the element may be in the left or right subarray after rotation.

• Return the index of the element if found, else return -1.

Check if two strings are anagrams by rearranging their letters.

• Create a frequency map of characters for both strings

• Compare the frequency maps to check if they are equal

• Return True if the frequency maps are equal, else False

There are multiple ways to display HTML elements, including inline, block, inline-block, and flex.

• HTML elements can be displayed as inline, which allows them to flow with surrounding content.

• Block elements take up the full width available and start on a new line.

• Inline-block elements are displayed as blocks, but flow like inline elements.

• Flexbox allows for more advanced layout options, such as aligning items and distributing space.

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.

Find the length of the longest substring without repeating characters in a given string.

• Use a sliding window approach to keep track of the longest substring without repeating characters.

• Use a hashmap to store the index of each character in the string.

• Update the start index of the window when a repeating character is encountered.

• Calculate the maximum length of the substring as you iterate through the string.

Function to simulate dice roll with equal probability without using random function

• Use a toss function that returns either 0 or 1 with equal probability

• Call the toss function 3 times and convert the result to a binary number

• If the binary number is greater than 0 and less than or equal to 6, return it

• If the binary number is greater than 6, repeat the process

Given three sorted arrays, find common elements.

• Create three pointers to traverse each array

• Compare the elements at the pointers and move the pointer of the smallest element

• If all pointers point to the same element, add it to the result and move all pointers

• Repeat until any pointer reaches the end of its array

Function to determine the order of integers in an array.

• Check first and last element to determine if increasing or decreasing

• Check for inflection point to determine if order changes

• Return order type as string

Design a database schema for a movie site with user ratings and recommendations.

• Create tables for movies, users, ratings, and recommendations

• Use foreign keys to link tables

• Include columns for movie genre and user watch history

• Algorithm for recommendations can use user watch history and ratings to suggest similar movies

Access specifiers define the level of access to class members in Object-Oriented Programming.

• Access specifiers include public, private, protected, and default

• Public members are accessible from outside the class

• Private members are only accessible within the class

• Protected members are accessible within the class and its subclasses

• Default access is when no access specifier is specified

Optimizing website asset loading involves minimizing file sizes, reducing HTTP requests, utilizing caching, and prioritizing critical resources.

• Minimize file sizes by compressing images, scripts, and stylesheets.

• Reduce HTTP requests by combining files, using sprites, and lazy loading non-essential resources.

• Utilize browser caching to store static assets locally for faster subsequent page loads.

• Prioritize critical resources like above-the-fold content to ensure faster renderin...read more

Abstraction is hiding the implementation details while inheritance is a mechanism for creating new classes using existing classes.

• Abstraction focuses on hiding the internal implementation details of a class, allowing the user to only interact with the necessary information.

• Inheritance allows a class to inherit properties and behavior from another class, promoting code reusability and creating a hierarchy of classes.

• Abstraction is achieved through abstract classes and interfac...read more

Fill the 5-liter jar, pour it into the 3-liter jar, fill the 5-liter jar again, and pour enough to fill the 3-liter jar. This leaves 4 liters in the 5-liter jar.

• Fill the 5-liter jar

• Pour the 5 liters into the 3-liter jar

• Fill the 5-liter jar again

• Pour enough to fill the 3-liter jar

• 4 liters will be left in the 5-liter jar

Advantages of OOP include code reusability, modularity, and easier maintenance.

• Code reusability: Objects can be reused in different parts of the program, reducing redundancy.

• Modularity: OOP allows for breaking down complex problems into smaller, more manageable parts.

• Easier maintenance: Changes to one part of the codebase do not necessarily affect other parts, making maintenance easier.

• Encapsulation: Data hiding and abstraction help in protecting data and only exposing necess...read more

Measure 5 litres of water using 3 and 7 litre containers.

• Fill the 3 litre container completely

• Pour the water from the 3 litre container into the 7 litre container

• Fill the 3 litre container again and pour it into the 7 litre container until it is full

• The remaining water in the 3 litre container is 1 litre

• Empty the 7 litre container and pour the 1 litre water from the 3 litre container into it

• Fill the 3 litre container again and pour it into the 7 litre container

• The 7 litre con...read more

Left join returns all records from left table and matching records from right table. Full outer join returns all records from both tables.

• Left join is used to combine two tables based on a common column.

• In left join, all records from the left table are returned along with matching records from the right table.

• If there is no match in the right table, NULL values are returned.

• Example: SELECT * FROM table1 LEFT JOIN table2 ON table1.id = table2.id;

• Full outer join returns all rec...read more

Optimize images, minify code, reduce HTTP requests, use caching, and lazy loading.

• Optimize images using compression and appropriate file formats

• Minify code to reduce file size and improve load times

• Reduce HTTP requests by combining files and using sprites

• Use caching to store frequently accessed data locally

• Implement lazy loading to defer loading of non-critical resources

Event bubbling is the process where an event triggered on a child element is propagated up through its parent elements.

• In event bubbling, when an event occurs on a child element, it first runs the event handlers on the child element, then on its parent, then all the way up to the top level of the DOM.

• Event bubbling allows for delegation of event handling to a parent element, reducing the number of event listeners needed.

• To stop event bubbling, you can use the stopPropagation(...read more

A static variable in C is a variable that retains its value between function calls.

• Declared using the 'static' keyword

• Retains its value throughout the program's execution

• Useful for maintaining state across function calls

Magic functions are special methods in PHP that start with __. Autoloading is a way to automatically load classes.

• Magic functions are used to handle certain events in PHP, such as object creation or property access.

• Autoloading allows PHP to automatically load classes when they are needed, without requiring manual includes.

• Magic functions can be used in conjunction with autoloading to dynamically load classes or handle errors.

Function to check if two strings are anagram or not

• Create two character arrays from the strings

• Sort the arrays

• Compare the sorted arrays

Query to fetch duplicate email from table

• Use GROUP BY and HAVING clause to filter out duplicates

• SELECT email, COUNT(*) FROM table_name GROUP BY email HAVING COUNT(*) > 1;

• This will return all the duplicate emails in the table

The .on('click',function() is a more flexible method than .click(function())

• The .on() method can handle multiple events and selectors

• The .click() method can only handle one event and one selector

• The .on() method can also handle dynamically added elements

• The .click() method cannot handle dynamically added elements

Queue can be implemented using two stacks by maintaining the order of elements in the stacks.

• Create two stacks, let's call them stack1 and stack2

• When an element is enqueued, push it to stack1

• When an element is dequeued, pop all elements from stack1 and push them to stack2

• Pop the top element from stack2 and return it as the dequeued element

• If stack2 is empty, repeat step 3

• To get the front element of the queue, peek the top element of stack2

Check if a number is a power of 2 or not.

• A power of 2 has only one bit set in its binary representation.

• Use bitwise AND operator to check if the number is a power of 2.

• If n is a power of 2, then n & (n-1) will be 0.