Here are the important Questions for Interviews on DSA to understand, if you are going for interview where DSA questions will be asked then you can read these questions and get answers. Get Important Interview questions on DSA (Data Structures & Algorithms) here…

Interview Questions on DSA

What is DSA?

DSA stands for Data Structures and Algorithms. It’s the core of coding. Data Structures help store and organize data. Algorithms help solve problems using logic and steps.

Why is DSA important in coding interviews?

Because it shows how well you can think logically, solve problems, and write optimized code — something every company values.

What are the main types of Data Structures?

• Linear: Arrays, Linked Lists, Stacks, Queues
• Non-linear: Trees, Graphs
• Hash-based: Hash Tables, Hash Maps
• Others: Heaps, Tries, Sets

What is the difference between Stack and Queue?

• Stack uses Last In First Out (LIFO). Like a stack of plates.
• Queue uses First In First Out (FIFO). Like a queue at the ticket counter.

What is a Linked List?

A Linked List is a series of connected nodes. Each node holds data and a pointer to the next. Unlike arrays, the memory isn’t continuous.

What is the difference between Linear and Binary Search?

• Linear Search: Go through each element one by one. Time complexity O(n).
• Binary Search: Works on sorted arrays. Keep dividing the array. Time complexity O(log n).

What is Recursion?

Recursion is when a function calls itself. You must define a base case to stop it. Example: Calculating factorial or Fibonacci numbers.

What is the time complexity of operations in Array, Linked List, and HashMap?

• Access: Array – O(1), Linked List – O(n), HashMap – O(1)
• Insertion at end: Array – O(1), Linked List – O(1), HashMap – O(1)
• Deletion at start: Array – O(n), Linked List – O(1), HashMap – O(1)
• Search: Array – O(n), Linked List – O(n), HashMap – O(1)

What is Big O Notation? It represents the time/space complexity of an algorithm in the worst case.

• O(1): Constant time
• O(n): Linear time
• O(log n): Logarithmic time
• O(n^2): Quadratic time

What are some popular algorithms in interviews?

• Searching (Linear Search, Binary Search)
• Sorting (Bubble Sort, Merge Sort, Quick Sort)
• Recursion & Backtracking
• Tree Traversals (Inorder, Preorder, Postorder)
• Graph Algorithms (DFS, BFS)
• Dynamic Programming
• Two Pointer and Sliding Window Techniques

A sorting algorithm is an algorithm that puts elements of a list into an order. Here are the important Questions for Interviews on Sorting Algorithms to understand, if you are going for interview where Sorting Algorithms questions will be asked then you can read these questions and get answers. Get Important Interview questions on Sorting Algorithms here…

Interview Questions on Sorting Algorithms

What is Sorting?

Sorting means arranging data in a specific order – either ascending or descending. It helps in searching faster and organizing data better.

Why is Sorting important in interviews?

Sorting is often the first step before applying other algorithms like binary search, and it’s a great way to check logic, optimization, and implementation skills.

What are the different types of Sorting Algorithms?

• Bubble Sort
• Selection Sort
• Insertion Sort
• Merge Sort
• Quick Sort
• Heap Sort
• Counting Sort
• Radix Sort

What is Bubble Sort?

It compares adjacent elements and swaps them if they’re in the wrong order. It “bubbles” the largest to the end.
Time Complexity: O(n²)

What is Selection Sort?

It selects the smallest element from the unsorted part and puts it in the correct position.
Time Complexity: O(n²)

What is Insertion Sort?

It builds the final sorted array one item at a time. Works like sorting playing cards in your hand.
Time Complexity: O(n²)

What is Merge Sort?

It divides the array into halves, sorts each half, and then merges them.
Time Complexity: O(n log n)

It’s a stable sort and great for large datasets.

What is Quick Sort?

It picks a pivot, partitions the array around the pivot, and recursively sorts.

Time Complexity: Best/Average: O(n log n), Worst: O(n²)

It’s faster than merge sort in practice but not stable.

What is Heap Sort?

It uses a binary heap data structure. It’s efficient and doesn’t need extra space.

Time Complexity: O(n log n)

What is the difference between Stable and Unstable Sorting?

Stable Sort: Keeps original order of equal elements (like Merge Sort).

Unstable Sort: Doesn’t guarantee order (like Quick Sort).

Which Sorting Algorithms are used in real life or libraries?

Python uses Timsort (a mix of Merge and Insertion Sort).

Java uses Merge Sort for objects.

C++ STL uses IntroSort (Hybrid of Quick + Heap + Insertion).

Here are the important Questions for Interviews on Mysql to understand, if you are going for interview where Mysql questions will be asked then you can read these questions and get answers. Get Important Interview questions on Mysql database here…

Mysql Interview Questions And Answers

Questions : 1 how to do login in mysql with unix shell.
Answers :1 By below method if password is pass and user name is root
# [mysql dir]/bin/mysql -h hostname -u root -p pass

Questions : 2 how you will Create a database on the mysql server with unix shell.  
Answers : 2 mysql> create database databasename;

Questions : 3 how to list or view all databases from the mysql server.
Answers : 3 mysql> show databases;

Questions : 4 How Switch (select or use) to a database.
Answers : 4 mysql> use databasename;

Questions : 5 How To see all the tables from a database of mysql server.
Answers : 5 mysql> show tables;

Questions : 6 How to see table’s field formats or description of table .
Answers : 6 mysql> describe tablename;

Questions : 7 How to delete a database from mysql server.
Answers : 7 mysql> drop database databasename;

Questions : 8 How we get Sum of column.
Answers : 8 mysql> SELECT SUM(*) FROM [table name];

Questions : 9 How to delete a table.
Answers : 9 mysql> drop table tablename;

Questions : 10 How you will Show all data from a table.
Answers : 10 mysql> SELECT * FROM tablename;

Questions : 11 How to returns the columns and column information pertaining to the designated table.
Answers : 11 mysql> show columns from tablename;

Questions : 12 How to Show certain selected rows with the value “abcd”.
Answers : 12 mysql> SELECT * FROM tablename WHERE fieldname = “abcd”;

Questions : 13 How will Show all records containing the name “sonia” AND the phone number ‘9899000000’.
Answers : 13 mysql> SELECT * FROM tablename WHERE name = “sonia” AND phone_number = ‘9899000000’;

Questions : 14 How you will Show all records not containing the name “sonia” AND the phone number ‘9899000000’ order by the phone_number field.
Answer : 14 mysql> SELECT * FROM tablename WHERE name != “sonia” AND phone_number = ‘9899000000’ order by phone_number;

Questions : 15 How to Show all records starting with the letters ‘sonia’ AND the phone number ‘9899000000’.
Answers : 15 mysql> SELECT * FROM tablename WHERE name like “sonia%” AND phone_number = ‘9899000000’;

Questions : 16 How to show all records starting with the letters ‘sonia’ AND the phone number ‘9899000000’ limit to records 1 through 5.
Answers : 16 mysql> SELECT * FROM tablename WHERE name like “sonia%” AND phone_number = ‘9899000000’ limit 1,5;

Questions : 16 Use a regular expression to find records. Use “REGEXP BINARY” to force case-sensitivity. This finds any record beginning with r.
Answer : 16 mysql> SELECT * FROM tablename WHERE rec RLIKE “^r”;

Questions : 17 How you will Show unique records.
Answer : 17 mysql> SELECT DISTINCT columnname FROM tablename;

Questions : 18 how we will Show selected records sorted in an ascending (asc) or descending (desc).
Answer : 18 mysql> SELECT col1,col2 FROM tablename ORDER BY col2 DESC;

mysql> SELECT col1,col2 FROM tablename ORDER BY col2 ASC;

Questions : 19 how to Return total number of rows.
Answers : 19 mysql> SELECT COUNT(*) FROM tablename;

Questions : 20 How to Join tables on common columns.
Answer : 20 mysql> select lookup.illustrationid, lookup.personid,person.birthday from lookup left join person on lookup.personid=person.personid=statement to join birthday in person table with primary illustration id.

Questions : 21 How to Creating a new user. Login as root. Switch to the MySQL db. Make the user. Update privs.
Answer : 21 # mysql -u root -p

mysql> use mysql;

mysql> INSERT INTO user (Host,User,Password) VALUES(‘%’,’username’,PASSWORD(‘password’));

mysql> flush privileges;

Questions : 22 How to Change a users password from unix shell.
Answers : 22 # [mysql dir]/bin/mysqladmin -u username -h hostname.blah.org -p password ‘new-password’

Questions : 23 How to Change a users password from MySQL prompt. Login as root. Set the password. Update privs.
Answer : 23 # mysql -u root -p

mysql> SET PASSWORD FOR ‘user’@’hostname’ = PASSWORD(‘passwordhere’);

mysql> flush privileges;

Questions : 24 How to Recover a MySQL root password. Stop the MySQL server process. Start again with no grant tables. Login to MySQL as root. Set new password. Exit MySQL and restart MySQL server.
Answer : 24 # /etc/init.d/mysql stop
# mysqld_safe –skip-grant-tables &
# mysql -u root
mysql> use mysql;
mysql> update user set password=PASSWORD(“newrootpassword”) where User=’root’;
mysql> flush privileges;
mysql> quit
# /etc/init.d/mysql stop
# /etc/init.d/mysql start

Questions : 25 How to Set a root password if there is on root password.
Answer : 25 # mysqladmin -u root password newpassword

Questions : 26 How to Update a root password.
Answer : 26 # mysqladmin -u root -p oldpassword newpassword

Questions : 27 How to allow the user “sonia” to connect to the server from localhost using the password “passwd”. Login as root. Switch to the MySQL db. Give privs. Update privs.
Answers : 27 # mysql -u root -p
mysql> use mysql;
mysql> grant usage on *.* to sonia@localhost identified by ‘passwd’;
mysql> flush privileges;

Questions : 28 How to give user privilages for a db. Login as root. Switch to the MySQL db. Grant privs. Update privs.
Answers : 28 # mysql -u root -p
mysql> use mysql;
mysql> INSERT INTO user (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,Create_priv,Drop_priv) VALUES (‘%’,’databasename’,’username’,’Y’,’Y’,’Y’,’Y’,’Y’,’N’);
mysql> flush privileges;
or
mysql> grant all privileges on databasename.* to username@localhost;
mysql> flush privileges;

Questions : 29 How To update info already in a table and Delete a row(s) from a table.
Answer : 29 mysql> UPDATE [table name] SET Select_priv = ‘Y’,Insert_priv = ‘Y’,Update_priv = ‘Y’ where [field name] = ‘user’;
mysql> DELETE from [table name] where [field name] = ‘whatever’;

Questions : 30 How to Update database permissions/privilages.
Answer : 30 mysql> flush privileges;

Questions : 31 How to Delete a column and Add a new column to database.
Answer : 31 mysql> alter table [table name] drop column [column name];
mysql> alter table [table name] add column [new column name] varchar (20);

Questions : 32 Change column name and Make a unique column so we get no dupes.
Answer : 32 mysql> alter table [table name] change [old column name] [new column name] varchar (50);
mysql> alter table [table name] add unique ([column name]);

Questions : 33 How to make a column bigger and Delete unique from table.
Answer : 33 mysql> alter table [table name] modify [column name] VARCHAR(3);
mysql> alter table [table name] drop index [colmn name];

Questions : 34 How to Load a CSV file into a table.
Answer : 34 mysql> LOAD DATA INFILE ‘/tmp/filename.csv’ replace INTO TABLE [table name] FIELDS TERMINATED BY ‘,’ LINES TERMINATED BY ‘n’ (field1,field2,field3);

Questions : 35 How to dump all databases for backup. Backup file is sql commands to recreate all db’s.
Answer : 35 # [mysql dir]/bin/mysqldump -u root -ppassword –opt >/tmp/alldatabases.sql

Questions : 36 How to dump one database for backup.
Answer : 36 # [mysql dir]/bin/mysqldump -u username -ppassword –databases databasename >/tmp/databasename.sql

Questions : 37 How to dump a table from a database.
Answer : 37 # [mysql dir]/bin/mysqldump -c -u username -ppassword databasename tablename > /tmp/databasename.tablename.sql

Questions : 38 Restore database (or database table) from backup.
Answer : 38 # [mysql dir]/bin/mysql -u username -ppassword databasename < /tmp/databasename.sql

Questions : 39 How to Create Table show Example.
Answer : 39 mysql> CREATE TABLE [table name] (firstname VARCHAR(20), middleinitial VARCHAR(3), lastname VARCHAR(35),suffix VARCHAR(3),officeid VARCHAR(10),userid VARCHAR(15),username VARCHAR(8),email VARCHAR(35),phone VARCHAR(25), groups VARCHAR(15),datestamp DATE,timestamp time,pgpemail VARCHAR(255));

Questions : 40 How to search second maximum(second highest) salary value(integer)from table employee (field salary)in the manner so that mysql gets less load?
Answers : 40 By below query we will get second maximum(second highest) salary value(integer)from table employee (field salary)in the manner so that mysql gets less load?
SELECT DISTINCT(salary) FROM employee order by salary desc limit 1 , 1 ;
(This way we will able to find out 3rd highest , 4th highest salary so on just need to change limit condtion like LIMIT 2,1 for 3rd highest and LIMIT 3,1 for 4th
some one may finding this way useing below query that taken more time as compare to above query SELECT salary FROM employee where salary < (select max(salary) from employe) order by salary DESC limit 1 ;

Here are the important Questions for Interviews on Array to understand, if you are going for interview where array questions will be asked then you can read those questions and get answers. Get Important Interview questions on Array here…

Questions for Interviews on Array

What is an array?

An array is a data structure consisting of a collection of elements, each identified by at least one array index or key.

How do you declare an Array?

Each language has its own way of declaring arrays, but the general idea is similar: defining the type of elements and the number of elements or initializing it directly.

C/C++:
int arr[5];
This declares an array of 5 integers in C/C++.

Java:
int[] arr = new int[5];
This declares and initializes an array of 5 integers in Java.

Python:
arr = [1, 2, 3, 4, 5]
In Python, you use a list, which functions like an array, and it doesn’t require a fixed size.

JavaScript:
let arr = [1, 2, 3, 4, 5];
JavaScript uses arrays without needing a size specification at declaration.

C#:
int[] arr = new int[5];
In C#, this declares an array of 5 integers.

Can an array be resized at runtime?

An array is fixed in size once created. However, in C, you can resize an array at runtime using Dynamic Memory Allocation (DMA) with malloc or realloc. Most of the modern languages have dynamic sized arrays like vector in C++, list in Python and ArrayList in Java which automatically get resized.

Is it possible to declare an array without specifying its size?

In C/C++, declaring array without specifying its size is not allowed. Doing so will cause a compile-time error. However we can create a pointer in C and create memory dynamically using malloc(). In C++, we have vectors where we can do declaration first and then dynamically add elements. In modern languages like Java, Python and JavaScript, we can declare without specifying size.

What is the time complexity for accessing an element in an array?

The time complexity for accessing an element in an array is O(1), as it can be accessed directly using its index.

What is the difference between an array and a linked list?

An array is a static data structure, while a linked list is a dynamic data structure. Raw arrays have a fixed size, and elements are stored consecutively in memory, while linked lists can grow and do not require contiguous memory allocation. The dynamic sized arrays allow flexible size, but the worst case time complexity for insertion/deletion at the end becomes more than O(1). With linked list, we get worst case time complexity as O(1) for insertion and deletion.

How would you find out the smallest and largest element in an array?

Best approach is iterative (linear search) while the other two are recursive and sorting approach.
Iterative method

Algorithm:

1.Initialize two variables:
small = arr[0] (first element as the smallest)
large = arr[0] (first element as the largest)
2.Traverse through the array from index 1 to n-1.
3.If arr[i] > large, update large = arr[i].
4.If arr[i] < small, update small = arr[i].
5.Print the values of small and large.

include

using namespace std;

void findMinMax(int arr[], int n) {
int small = arr[0], large = arr[0];

for (int i = 1; i < n; i++) {
    if (arr[i] > large)  
        large = arr[i];
    if (arr[i] < small)  
        small = arr[i];
}

cout << "Smallest element: " << small << endl;
cout << "Largest element: " << large << endl;

}

int main() {
int arr[] = {7, 2, 9, 4, 1, 5};
int n = sizeof(arr) / sizeof(arr[0]);

findMinMax(arr, n);

return 0;

}

What is the time complexity to search in an unsorted and sorted array?

Unsorted Array: The time complexity for searching an element in an unsorted array is O(n), as we may need to check every element.

Sorted Array : The time complexity for searching an element in a sorted array is O(log n) using binary search

O(logn) takes less time than O(n) whereas O(nlogn) takes more time than O(n).

What are the time complexities to insert and delete at the beginning if we have extra space in the array for the new element?

Insert at Beginning: If we have extra space, the time complexity is O(n), as all the existing elements need to be shifted to make room for the new element.

Delete at Beginning: The time complexity is O(n), as all the remaining elements need to be shifted to fill the gap left by the deleted element.

What are the time complexities to insert and delete at the end if we have extra space in the array for the new element?

Insert at End: If there is extra space, the time complexity is O(1), as we can directly add the element at the end without shifting any other elements.

Delete at End: The time complexity is O(1), as removing the last element does not require shifting any elements