Common Interview Questions

1.
Given a rectangular (cuboidal for the puritans)
cake with a rectangular piece removed (any size or orientation), how would you
cut the remainder of the cake into two equal halves with one straight cut of a
knife ?

2.
You're given an array containing both positive
and negative integers and required to find the subarray with the largest sum
(O(N) a la KBL). Write a routine in C for the above.

3.
Given an array of size N in which every number
is between 1 and N, determine if there are any duplicates in it. You are allowed
to destroy the array if you like.

4.
Given an array of characters which form a
sentence of words, give an efficient algorithm to reverse the order of the
words (not characters) in it.

5.
How many points are there on the globe where by
walking one mile south, one mile east and one mile north you reach the place
where you started.

6.
In a X's and 0's game (i.e. TIC TAC TOE) if you
write a program for this give a fast way to generate the moves by the computer.
I mean this should be the fastest way possible.

7.
A version of the "There are three persons X
Y Z, one of which always lies"..

8.
There are 3 ants at 3 corners of a triangle,
they randomly start moving towards another corner.. what is the probability
that they don't collide.

9.
If you are on a boat and you throw out a
suitcase, Will the level of water increase.

10.
There are 4 men who want to cross a bridge. They
all begin on the same side. You have 17 minutes to get all of them across to
the other side. It is night. There is one flashlight. A maximum of two people
can cross at one time. Any party who crosses, either 1 or 2 people, must have
the flashlight with them. The flashlight must be walked back and forth, it
cannot be thrown, etc. Each man walks at a different speed. A pair must walk
together at the rate of the slower mans pace.

a.
Man 1:1 minute to cross

b.
Man 2: 2 minutes to cross

c.
Man 3: 5 minutes to cross

d.
Man 4: 10 minutes to cross

11.
You have 5 jars of pills. Each pill weighs 10
gram, except for contaminated pills contained in one jar, where each pill
weighs 9 gm. Given a scale, how could you tell which jar had the contaminated
pills in just one measurement?

12.
One train leaves Los Angeles at 15 MPH heading
for New York. Another train leaves from New York at 20mph heading for Los
Angeles on the same track. If a bird, flying at 25mph, leaves from Los Angeles
at the same time as the train and flies back and forth between the two trains
until they collide, how far will the bird have traveled?

13.
Imagine that you have 26 constants, labelled A
through Z. Each constant is assigned a value in the following way: A = 1; the
rest of the values equal their position in the alphabet (B corresponds to the
second position so it equals 2, C = 3, etc.) raised to the power of the
preceeding constant value. So, B = 2 ^ (A's value), or B = 2^1 = 2. C = 3^2 =
9. D = 4^9, etc., etc. Find the exact numerical value to the following
equation:

(X - A) * (X - B) * (X - C) * ... * (X - Y) * (X - Z)

14.
You have 12 balls. All of them are identical
except one, which is either heavier or lighter than the rest - it is either
hollow while the rest are solid, or solid while the rest are hollow. You have a
simple two-armed scale, and are permitted three weighings. Can you identify the
odd ball, and determine whether it is hollow or solid.

Programming questions that require thinking

1.
Write a routine to draw a circle (x ** 2 + y **
2 = r ** 2) without making use of any floating point computations at all.

2.
Given only putchar (no sprintf, itoa, etc.)
write a routine putlong that prints out an unsigned long in decimal.

3.
Give a one-line C expression to test whether a
number is a power of 2. [No loops allowed - it's a simple test.]

4.
Give a very good method to count the number of
ones in a 32 bit number. (caution: looping through testing each bit is not a
solution).

5.
What are the different ways to say, the value of
x can be either a 0 or a 1.

6.
I was given two lines of assembly code which
found the absolute value of a number stored in two's complement form. I had to
recognize what the code was doing.

7.
Give a fast way to multiply a number by 7.

8.
Write an efficient algo and C code to shuffle a
pack of cards.. this one was a feedback process until we came up with one with
no extra storage.

A real life problem - A square picture is cut into 16
sqaures and they are shuffled. Write a program to rearrange the 16 squares to
get the original big square.

Consider the base -2 representation of numbers. (-2 instead
of usual +2). Give the condition for a number represented in this form to be
positive? Also, if P(A, B) is a function that takes two 0-1 strings A,B in this
representation, when can we say that P(A,B) returns the sum of these two
numbers?

Given an expression tree with no parentheses in it, write
the program to give equivalent infix expression with parentheses inserted where
necessary.

Given a maze with cheese at one place and a mouse at some
entrance, write a program to direct the mouse to cheese correctly. (Assume
there is a path). Following primitives are given: moveforward, turnright,
turnleft, iswall?, ischeese?, eatcheese.

Give me an algorithm and C code to find the subarray with
the largest sum given an array containing both positive and negative integers.

Write a function that returns the factorial of a number.

Write a function that computes the nth number in the
Fibonacci sequence.

Write an implementation of strlen().

Switch the integer values stored in two registers without
using any additional memory.

Given two strings S1 and S2. Delete from S2 all those
characters which occur in S1 also and finally create a clean S2 with the
relevant characters deleted.

Write a small lexical analyzer - interviewer gave tokens.
expressions like "a*b" etc.

Write a routine that prints out a 2-D array in spiral order!

How is the readers-writers problem solved? - using
semaphores/ada .. etc.

Write code for reversing a linked list.

Write, efficient code for extracting unique elements from a
sorted list of array. e.g. (1, 1, 3, 3, 3, 5, 5, 5, 9, 9, 9, 9) -> (1, 3, 5,
9).

Microsoft question

Given a rectangular (cuboidal for the puritans) cake with a
rectangular piece removed (any size or orientation), how would you cut the
remainder of the cake into two equal halves with one straight cut of a knife ?

You're given an array containing both positive and negative
integers and required to find the subarray with the largest sum (O(N) a la
KBL). Write a routine in C for the above.

Given an array of size N in which every number is between 1
and N, determine if there are any duplicates in it. You are allowed to destroy
the array if you like.[I ended up giving about 4 or 5 different solutions for
this, each supposedly better than the others ].

Write a routine to draw a circle (x ** 2 + y ** 2 = r ** 2)
without making use of any floating point computations at all. [ This one had me
stuck for quite some time and I first gave a solution that did have floating
point computations ].

Given only putchar (no sprintf, itoa, etc.) write a routine
putlong that prints out an unsigned long in decimal. [ I gave the obvious
solution of taking % 10 and / 10, which gives us the decimal value in reverse
order. This requires an array since we need to print it out in the correct
order. The interviewer wasn't too pleased and asked me to give a solution which
didn't need the array ].

Give a one-line C expression to test whether a number is a
power of 2. [No loops allowed - it's a simple test.]

Given an array of characters which form a sentence of words,
give an efficient algorithm to reverse the order of the words (not characters)
in it.

How many points are there on the globe where by walking one
mile south, one mile east and one mile north you reach the place where you
started.

Give a very good method to count the number of ones in a 32
bit number. (caution: looping through testing each bit is not a solution).

What are the different ways to say, the value of x can be
either a 0 or a 1. Apparently the if then else solution has a jump when written
out in assembly. if (x == 0) y=0 else y =x

(a-1) xor a == 0 - What does this do?

How can you print singly linked list in reverse order? (it's
a huge list and you cant use recursion)

How can you find out if there is a loop in a very long list?

A character set has 1 and 2 byte characters. One byte
characters have 0 as the first bit. You just keep accumulating the characters
in a buffer. Suppose at some point the user types a backspace, how can you
remove the character efficiently. ( Note: You cant store the last character
typed because the user can type in arbitrarily many backspaces)

How would you reverse the bits of a number with log N
arithmetic operations, where N is the number of bits in the integer (eg
32,64..)

Whats the simples way to check if the sum of two unsigned
integers has resulted in an overflow.

Induction on i:1..n: Maintain the subarray with largest sum
and suffix with largest sum and then update both after adding the i+1th
element...

Sum of the numbers or copy i into A[i] so on till conflict.

Update deltaY while incrementing x. Have to multiply so that
the deltay is not a floating pt number.

Find the largest 10**n less than given number, then div etc.

Infinite.

Shivku said this question is garbled thru ages.

reverse the pointers till you reach the end and
print-and-reverse as you return.

Have two 'threads' one at twice the speed of the other
traversing the list and see if at anytime they meet.

Scan the bytes backward till you reach one with the first
bit set to 0. Now this is either a one byte character or the second byte of a
two byte one. Either way it marks a Character boundary. Start from there an
scan forward to find what the last character is.

Flip adjacent bits, then flip adjacent 2 bit sets, then
4-bits and so on. Each of this swap can be done in constant time using
appropriate masks and shifts.

if (a+b) < a or (a+b) < b then overflow has occurred

Data structures and algorithms questions

Write a function and the node data structure to visit all of
the nodes in a binary tree.

You know what a queue is .... Implement a queue class with
Java. What is the cost of enqueue and dequeue? Can you improve this? What if
the queue is full (I was using an looping array)? What kind of mechanism would
you use to increase its size?

Give an algorithm that calculates the distance between two
text strings (only operations you can have are: delete, add, and change, one by
one).

Given the definition of a sequence (5 4 7 6 is, but 1 2 4 5
is not), write an algorithm to check if an arbitrary array is a sequence or
not. Once I figured out a solution, I was asked to do a space and time
complexity analysis.

Describe a situation where concurrent access would lead to
inconsistency in your application. How would you solve this problem?

You are given a list of n numbers from 1 to n-1, with one of
the numbers repeated. Devise a method to determine which number is repeated.

Write an algorithm to detect loop in a linked list.

Given the time, devise an algorithm to calculate the angle
between the hour and minute hands of an analog clock.

Devise an algorithm for detecting whether a given string is
a palindrome (spelled the same way forwards and backwards). For example,
"A man, a plan, a canal, Panama."

Given an eight-bit bitmap graphics file, devise an algorithm
to convert the file into a two-bit ASCII approximation.

Reverse a linked list.

Insert in a sorted list

First some definitions for this problem: a) An ASCII
character is one byte long and the most significant bit in the byte is always
'0'. b) A Kanji character is two bytes long. The only characteristic of a Kanji
character is that in its first byte the most significant bit is '1'. Now you
are given an array of a characters (both ASCII and Kanji) and, an index into
the array. The index points to the start of some character. Now you need to
write a function to do a backspace (i.e. delete the character before the given
index).

Delete an element from a doubly linked list.

Write a function to find the depth of a binary tree.

Assuming that locks are the only reason due to which
deadlocks can occur in a system. What would be a foolproof method of avoiding
deadlocks in the system.

Besides communication cost, what is the other source of
inefficiency in RPC?

Ways of optimizing symbol table storage in compilers.

A walk-through through the symbol table functions, lookup()
implementation etc - The interv. was on the Microsoft C team.

Given an array t[100] which contains numbers between 1..99.
Return the duplicated value. Try both O(n) and O(n-square).

Given an array of characters. How would you reverse it. ?
How would you reverse it without using indexing in the array.

Given a sequence of characters. How will you convert the
lower case characters to upper case characters. ( Try using bit vector - sol
given in the C lib -> typec.h)

Give a good data structure for having n queues ( n not
fixed) in a finite memory segment. You can have some data-structure separate
for each queue. Try to use at least 90% of the memory space.

Do a breadth first traversal of a tree.

Given a list of numbers ( fixed list) Now given any other
list, how can you efficiently find out if there is any element in the second
list that is an element of the first list (fixed list).

What is a balanced tree

How would you find a cycle in a linked list? Try to do it in
O(n) time. Try it using a constant amount of memory.

Implement an algorithm to reverse a doubly linked list.

A square picture is cut into 16 squares and they are
shuffled. Write a program to rearrange the 16 squares to get the original big
square.

The Web can be modeled as a directed graph. Come up with a
graph traversal algorithm. Make the algorithm non-recursive and breadth-first.

How would you implement a hash table ? How do you deal with
collisions?

How would you find a cycle in a linked list? Try to do it in
O(n) time. Try it using a constant amount of memory.

Given a history of URLs, how would you determine if a
particular URL had been seen before?

Since pages can have multiple URLs pointing to them, how can
you make sure you've never seen the same CONTENT before?

Write a function to print all of the permutations of a
string.

Come up with the plan on how to traverse a graph, as well as
to quickly determine if a given URL is one of the million or so you've
previously seen.

The Web can be modeled as a directed graph. Come up with a
graph traversal algorithm. Make the algorithm non-recursive and breadth-first.

Implement an algorithm to reverse a singly linked list.
(with and without recursion)

Implement an algorithm to reverse a doubly linked list.

Implement an algorithm to insert in a sorted list.

Delete an element from a doubly linked list.

Write a function to copy two strings, A and B. The last few
bytes of string A overlap the first few bytes of string B.

Implement an algorithm to sort an array.

Given a sequence of characters, how will you convert the
lower case characters to upper case characters?

Write a routine that prints out a 2-D array in spiral order.

Count the number of set bits in a number without using a
loop.

Give me an algorithm and C code to shuffle a deck of cards,
given that the cards are stored in an array of ints. Try to come up with a
solution that does not require any extra space.

Write a function that takes in a string parameter and checks
to see whether or not it is an integer, and if it is then return the integer
value.

How would you print out the data in a binary tree, level by
level, starting at the top?

Given an array of characters which form a sentence of words,
give an efficient algorithm to reverse the order of the words in it.

Write a function to find the depth of a binary tree.

Given a list of numbers ( fixed list) Now given any other
list, how can you efficiently find out if there is any element in the second
list that is an element of the first list (fixed list).

How would you implement a queue from a stack?

Write a funtion that finds repeating characters in a string.

Write a routine to reverse a series of numbers without using
an array.

Give me an algorithm for telling me the number I didn't give
you in a given range of numbers. (Numbers are given at random)

From CSRI

Write a function to check if two rectangles defined as below
overlap or not.

struct rect {

int top, bot, left, right;

} r1, r2;

Write a program to print the elements of a very long linked
list in ascending order. There may be duplicates in the list. You cannot modify
the list or create another one. Memory is tight, speed is not a problem.

Write a function to reverse a singly linked list, given
number of links to reverse.

Write a function to convert an int to a string.

Some weird problem on vector calculus with some
transformation matrices being applied - need paper and pencil to describe it.

Given ships travel between points A and B, one every hour
leaving from both ends (simultaneously), how many ships are required (minimum),
if the journey takes 1hr 40 mts. How many ships does each ship encounter in its
journey, and at what times?

Write a SetPixel(x, y) function, given a pointer to the
bitmap. Each pixel is represented by 1 bit. There are 640 pixels per row. In
each byte, while the bits are numbered right to left, pixels are numbered left
to right. Avoid multiplications and divisions to improve performance.

How do you represent an n-ary tree? Write a program to print
the nodes of such a tree in breadth first order.

Write the 'tr' program of UNIX. Invoked as

tr -str1 -str2.

It reads stdin and prints it out to stdout, replacing every
occurance of str1[i] with str2[i]. eg.

tr -abc -xyz

to be and not to be
<- input="" p="">

to ye xnd not to ye
<- output="" p="">

C syntax, semantics and simple programming questions

What does the term cast refer to? Why is it used?

In arithmetic expressions, to what data type will the C
compiler promote a character?

What is the difference between a statement and a block?

Increment the variable next three different ways.

How is a comment formed in C.

Can comments be nested?

From the standpoint of programming logic, what is the difference
between a loop with the test at the top, and a loop where the test is at the
bottom?

Specify the skeletons of two C loops with the test at the
top.

Specify a C loop with the test at the bottom.

What is the switch statement?

What does a break statement do? Which control structures use
it?

In a loop, what is the difference between a break and
continue statement?

Where may variables be defined in C?

What is the difference between a variable definition and a
variable declaration?

What is the purpose of a function prototype?

What is type checking?

To what does the term storage class refer?

List C's storage classes and what they signify.

State the syntax for the printf() and scanf() functions.
State their one crucial difference with respect to their parameters.

With respect to function parameter passing, what is the
difference between call-by-value and call-by-reference? Which method does C
use?

What is a structure and a union in C?

Define a structure for a simple name/address record.

What does the typedef keyword do?

Use typedef to make a short-cut way to declare a pointer to
the nameAddr structure above. Call it addrPtr.

Declare a variable with addrPtr called address.

Assuming the variable address above, how would one refer to
the city portion of the record within a C expression?

What is the difference between: #include and
#include "stdio.h"

What is #ifdef used for?

How do you define a constant in C?

Why can't you nest structure definitions?

Can you nest function definitions?

What is a forward reference?

What are the following and how do they differ: int, long,
float and double?

Define a macro called SQR which squares a number.

Is it possible to take the square-root of a number in C. Is
there a square-root operator in C?

Using fprintf() print a single floating point number
right-justified in a field of 20 spaces, no leading zeros, and 4 decimal
places. The destination should be stderr and the variable is called num.

What is the difference between the & and &&
operators and the | and || operators?

What is the difference between the -> and . operators?

What is the symbol for the modulus operator?

From the standpoint of logic, what is the difference between
the fragment:

if (next < max)

next++;

else

next = 0;

and the fragment:

next += (next < max)? (1):(-next);

What does the following fragment do?

while((d=c=getch(),d)!=EOF&&(c!='\t'&&c!='
'&&c!='\b')) *buff++ = ++c;

Is C case sensitive (ie: does C differentiate between upper
and lower case letters)?

Specify how a filestream called inFile should be opened for
random reading and writing. the file's name is in fileName.

What does fopen() return if successful. If unsuccessful?

What is the void data type? What is a void pointer?

Declare a pointer called fnc which points to a function that
returns an unsigned long.

Declare a pointer called pfnc which points to a function
that returns a pointer to a structure of type nameAddr.

It is possible for a function to return a character, an
integer, and a floating point number. Is it possible for a function to return a
structure? Another function?

What is the difference between an lvalue and an rvalue?

Given the decimal number 27, how would one express it as a
hexadecimal number in C?

What is malloc()?

What is the difference between malloc() and calloc()?

What kind of problems was C designed to solve?

write C code for deleting an element from a linked listy
traversing a linked list efficient way of elimiating duplicates from an array

Declare a void pointer

Make the pointer aligned to a 4 byte boundary in a efficient
manner

What is a far pointer (in DOS)

Write an efficient C code for 'tr' program. 'tr' has two
command line arguments. They both are strings of same length. tr reads an input
file, replaces each character in the first string with the corresponding
character in the second string. eg. 'tr abc xyz' replaces all 'a's by 'x's,
'b's by 'y's and so on.

Write C code to implement strtok() 'c' library function.

Implement strstr(), strcpy(), strtok() etc

Reverse a string.

Given a linked list which is sorted, how will you insert in
sorted way.

Write a function that allocates memory for a two-dimensional
array of given size (parameter x & y)

Write source code for printHex(int i) in C/C++

Write a function that finds the last instance of a character
in a string.

C++ syntax, semantics and concepts questions

What is an object in C++?

What is a message?

What is a class?

What is an instance?

What is a super-class?

What is inheritance?

To what does message protocol refer?

What is polymorphism?

What are instance variables?

What are class variables?

What is a method?

In C++ what is a constructor? A destructor?

Compare and contrast C and C++.

What is operator overloading?

What is cin and cout?

Contrast procedural and object oriented programming.

How do you link a C++ program to C functions?

Explain the scope resolution operator.

What are the differences between a C++ struct and C++ class?

How many ways are there to initialize an int with a
constant?

How does throwing and catching exceptions differ from using
setjmp and longjmp?

What is your reaction to this line of code?

delete this;

What is a default constructor?

What is a conversion constructor?

What is the difference between a copy constructor and an
overloaded assignment operator?

When should you use multiple inheritance?

What is a virtual destructor?

Explain the ISA and HASA class relationships. How would you
implement each in a class design?

When is a template a better solution than a base class?

What is the result of compiling this program in a C
compiler? in a C++ compiler?

int __ = 0;

main() {

int ___ = 2;

printf("%d\n", ___ + __);

}

What is the difference between C and C++ ? Would you prefer
to use one over the other ?

What are the access privileges in C++ ? What is the default
access level ?

What is data encapsulation ?

What is inheritance ?

What is multiple inheritance ? What are it's advantages and
disadvantages ?

What is polymorphism?

What do the keyword static and const signify ?

How is memory allocated/deallocated in C ? How about C++ ?

What is UML ?

What is the difference between a shallow copy and a deep
copy ?

What are the differences between new and malloc?

What is the difference between delete and delete[]?

What are the differences between a struct in C and in C++?

What are the advantages/disadvantages of using #define?

What are the advantages/disadvantages of using inline and
const?

What is the difference between a pointer and a reference?

When would you use a pointer? A reference?

What does it mean to take the address of a reference?

What does it mean to declare a function or variable as
static?

What is the order of initalization for data?

What is name mangling/name decoration?

What kind of problems does name mangling cause?

How do you work around them?

What is a class?

What are the differences between a struct and a class in
C++?

What is the difference between public, private, and
protected access?

For class CFoo { }; what default methods will the compiler
generate for you>?

How can you force the compiler to not generate them?

What is the purpose of a constructor? Destructor?

What is a constructor initializer list?

When must you use a constructor initializer list?

What is a: Constructor? Destructor? Default constructor?
Copy constructor? Conversion constructor?

What does it mean to declare a... member function as
virtual? member function as static? member varible as static? destructor as
static?

Can you explain the term "resource acqusition is
initialization?"

What is a "pure virtual" member function?

What is the difference between public, private, and
protected inheritance?

What is virtual inheritance?

What is placement new?

What is the difference between operator new and the new
operator?

What is exception handling?

Explain what happens when an exception is thrown in C++.

What happens if an exception is not caught?

What happens if an exception is throws from an object's
constructor?

What happens if an exception is throws from an object's
destructor?

What are the costs and benefits of using exceptions?

When would you choose to return an error code rather than
throw an exception?

What is a template?

What is partial specialization or template specialization?

How can you force instantiation of a template?

What is an iterator?

What is an algorithm (in terms of the STL/C++ standard
library)?

What is std::auto_ptr?

What is wrong with this statement? std::auto_ptr ptr(new
char[10]);

It is possible to build a C++ compiler on top of a C
compiler. How would you do this?