Mastercard interview prep

DSAEasy

An array holds the numbers from 1 to 8 with exactly one missing: [3, 7, 1, 2, 8, 4, 5]. Using the formula for the sum 1 + 2 + ... + n, which number is missing?

1. 5
2. 9
3. 4
4. 6

This topic is named in a candidate’s interview report: SDE on-campus interview, 2024, on GeeksforGeeks.

DSAMedium

You reverse a singly linked list in place by walking it once with three pointers, prev, curr and next. At each node, what do you do?

1. Save next = curr.next, point curr.next at prev, then move prev to curr and curr to next
2. Swap the node's value with the value at the other end of the list
3. Push every node onto a stack, then pop them all
4. Point curr.next at curr.next.next

This topic is named in a candidate’s interview report: SDE intern interview, 2024, on GeeksforGeeks.

DSAEasy

A singly linked list is circular if its last node points back to the head. How do you check that with no extra memory?

1. Walk from head.next until you reach null (not circular) or the head again (circular)
2. Count the nodes and compare with a stored length
3. Sort the list and look for duplicates
4. Check whether the head's value appears twice

This topic is named in a candidate’s interview report: SDE intern interview, 2024, on GeeksforGeeks.

DSAEasy

Scanning [12, 35, 1, 10, 34, 1] once while keeping the largest and the second largest distinct values, what is the second largest?

1. 35
2. 34
3. 12
4. 10

This topic is named in a candidate’s interview report: SDE on-campus interview, 2024, on GeeksforGeeks.

JavaMedium

What does this print?

public class Main {
    public static void main(String[] args) {
        String a = "ust";
        String b = "ust";
        String c = new String("ust");
        System.out.println((a == b) + " " + (a == c) + " " + a.equals(c));
    }
}

1. true true true
2. true false false
3. false false true
4. true false true

This topic is named in a candidate’s interview report: SDE intern interview, 2024, on GeeksforGeeks.

JavaMedium

Two threads call a synchronized method on the same Java object at the same moment. What happens?

1. Both run it together
2. One thread takes the object's lock and runs it; the other waits until the lock is released
3. The second call is dropped
4. Java throws a ConcurrentModificationException

This topic is named in a candidate’s interview report: SDE on-campus interview, 2024, on GeeksforGeeks.

JavaEasy

Why is Java called platform independent?

1. Java programs need no runtime
2. javac compiles to bytecode, and any machine with a JVM runs the same .class files
3. Java source is compiled again on every machine
4. Java can only run in a browser

This topic is named in a candidate’s interview report: SDE on-campus interview, 2022, on GeeksforGeeks.

PythonEasy

What does this print?

def is_rotation(a, b):
    return len(a) == len(b) and b in a + a

print(is_rotation("waterbottle", "erbottlewat"), is_rotation("abc", "acb"))

1. True True
2. True False
3. False True
4. False False

This topic is named in a candidate’s interview report: SDE intern interview, 2024, on GeeksforGeeks.

PythonEasy

Why does indentation matter in Python but not in C?

1. It is only a style rule in both
2. Python marks a block by its indentation, where C uses braces; a wrongly indented line changes which block it belongs to, or is an IndentationError
3. C forbids indentation
4. Python ignores indentation inside functions

This topic is named in a candidate’s interview report: SDE on-campus interview, 2022, on GeeksforGeeks.

DBMS and SQLMedium

When is a document database such as MongoDB usually a better fit than a relational database?

1. When many tables must be joined with strict transactions across them
2. When the data is a few small tables with a fixed structure
3. Whenever the data must survive a restart
4. When each record is read and written as a whole and its fields vary from record to record

This topic is named in a candidate’s interview report: SDE on-campus interview, 2022, on GeeksforGeeks.

DBMS and SQLMedium

What does adding an index on a column usually do?

1. Speeds up queries that search or sort on that column, at the cost of extra storage and slower inserts and updates
2. Speeds up every query on the table, with no cost
3. Prevents duplicate values in the column
4. Compresses the table to save space

This topic is named in a candidate’s interview report: SDE on-campus interview, 2024, on GeeksforGeeks.

DBMS and SQLMedium

What does a FULL OUTER JOIN of tables A and B return?

1. Only rows that match in both
2. Every row from both tables: matched rows joined, and unmatched rows from either side with NULLs for the other side's columns
3. Every row from A only
4. Every combination of rows from A and B

This topic is named in a candidate’s interview report: SDE on-campus interview, 2022, on GeeksforGeeks.

DBMS and SQLEasy

What is a stored procedure?

1. A backup of a table
2. A query the database runs automatically when a row changes
3. A named block of SQL saved in the database, run with a call and able to take parameters
4. An index on a view

This topic is named in a candidate’s interview report: SDE on-campus interview, 2022, on GeeksforGeeks.

DBMS and SQLMedium

A book can have several authors and an author can write several books. How do you model that in a relational database?

1. Put an author_id column in books
2. A third table, book_author(book_id, author_id), with a foreign key to each table and the pair as its primary key
3. Put a book_id column in authors
4. Store the author names as a list in one column of books

This topic is named in a candidate’s interview report: SDE on-campus interview, 2024, on GeeksforGeeks.

DBMS and SQLMedium

Table a holds the values 1, 2, 2 and table b holds 2, 3. How many rows do the two queries return?

SELECT v FROM a UNION SELECT v FROM b;
SELECT v FROM a UNION ALL SELECT v FROM b;

1. 3 and 5
2. 3 and 3
3. 5 and 5
4. 2 and 5

This topic is named in a candidate’s interview report: SDE on-campus interview, 2022, on GeeksforGeeks.

Operating systemsMedium

How does a mutex differ from a counting semaphore?

1. A mutex lets one holder in at a time and is released by its owner; a semaphore allows up to N and anyone may signal it
2. They are two names for the same thing
3. A semaphore can only be used between processes
4. A mutex lets N threads in at once

This topic is named in a candidate’s interview report: SDE on-campus interview, 2024, on GeeksforGeeks.

Operating systemsEasy

Which statement about stack and heap memory is true?

1. The stack holds each call's frame (locals, return address) and is freed when the call returns; the heap holds memory allocated at run time that lives until it is freed or collected
2. Heap memory is freed automatically when a function returns
3. The stack is always larger than the heap
4. Only global variables live on the stack

This topic is named in a candidate’s interview report: SDE intern on-campus interview, 2023, on GeeksforGeeks.

Computer networksMedium

Which HTTP method is NOT idempotent?

1. GET
2. PUT
3. DELETE
4. POST

This topic is named in a candidate’s interview report: SDE on-campus interview, 2024, on GeeksforGeeks.

Web developmentEasy

In React, how do props differ from state?

1. They are the same object
2. Props are passed in by the parent and read-only to the child; state is owned by the component and changed with its setter, which re-renders it
3. State is passed in by the parent; props are private
4. Props can only hold strings

This topic is named in a candidate’s interview report: SDE intern on-campus interview, 2023, on GeeksforGeeks.

Web developmentMedium

What is React's virtual DOM for?

1. It is a second browser that runs React
2. React renders to a lightweight tree in memory, compares it with the previous one, and applies only the differences to the real DOM
3. It stores the page offline
4. It makes React run on the server only

This topic is named in a candidate’s interview report: SDE intern on-campus interview, 2023, on GeeksforGeeks.