Find Output for this C Program

Problem:

What would be the output of the following C program? (Is it a valid C program?)


Explanation:

This will produce output “4321”. The return type of printf is “int” which is the number of characters written to stdout.


Cheers!!
Jack

C - %n format specifier in printf

Well, what does the format specifier %n of printf function do?

Explanation:
Print nothing, but write number of characters successfully written so far into an integer pointer parameter.

Example:

Output:
blah blah
val = 38

Cheers!
Jack

C program to determine endian'ess

We shall see a small C program to determine whether a machine's type is little-endian or big-endian.

Definition:

BigEndian means that the higher order byte of the number is stored in memory at the lowest address, and the lower order byte at the highest address. The big end comes first.

eg: OAOBOCOD will be stored as OA(a) OB(a+1) OC(a+2) OD(a+3)

LittleEndian means that the lower order byte of the number is stored in memory at the lowest address, and the higher order byte is stored at the highest address i.e., the little
end comes first.

eg: OAOBOCOD will be stored as OD(a) OC(a+1) OB(a+2) OA(a+3)

Program:


Cheers!!
Jack

Addition without using the + operator in C

Write a C function which does the addition of two integers without using the '+' operator. You can use only the bitwise operators.(Remember the good old method of implementing the full-adder circuit using the OR and XOR gates....)

Now, for the code implemented in C.

Cheers!
Jack

CAT Brain Teaser

Well, this can be considered off-topic. A brain teaser in CAT. Only 2% students were able to solve this in the CAT Exam. They should have been really sick :) Enough build up, lets see what the problem is.

Given,

5+3+2 = 151022
9+2+4 = 183652
8+6+3 = 482466
5+4+5 = 202541

Then, 7+2+5 = ???


Solution:

5+3+2 = (5*3)(5*2)(5*3 + 5*2 - 3)
9+2+4 = (9*2)(9*4)(9*2 + 9*4 - 2)
8+6+3 = (8*6)(8*3)(8*6 + 8*3 - 6)
5+4+5 = (5*4)(5*5)(5*4 + 5*5 - 4)

Hence,

7+2+5 = (7*2)(7*5)(7*2 + 7*5 - 2) = 143547

Cheers!!
Jack

"Offsetof" Macros in C : What it is and why it is

Problem:

The following is the offset macros which is used many a times. Lets figure out what is it trying to do and what is the advantage of using it.


Explanation:

offsetof tells you where in the memory allocation of the structure you will find a particular member.

Consider the example,


The structure defined takes up 12 bytes:

* byte 0: singlechar
* byte 1: arraymember[0]
* byte 2: arraymember[1]
* byte 3: arraymember[2]
* ...
* byte 10: arraymember[9]
* byte 11: anotherchar

The output will be:

offsetof(mystruct,singlechar) is 0
offsetof(mystruct,arraymember) is 1
offsetof(mystruct,anotherchar) is 11

If you allocate an object of type, and get a byte* to the start of the structure, you can use offsetof to find out where each member is. If you use that pointer offset, and convert it back to the correct type, it will give you a pointer to the member.


The output will be:

anotherchar is 17

The reason you can't assume that each member will be a specific offset from the beginning of the struct is complicated, and compiler dependent. If you must do something like this (which is really low-level stuff which you should avoid unless you have to), then use a macro like offsetof, rather than trying to manually specify the offset yourself.

Hope you learnt something.

Cheers!!
Jack

How to find angle between hour and minute hands in an analog clock?

Given a simple clock, we have to find the angle between the hour and minute hands. Since this is a deliberate question, we should obviously be ignoring the thickness of the hands in the clock.

We need to understand the following things before we arrive at our solution.

• The hour hand moves at the rate of 0.5 degrees per minute.
• The minute hand moves at the rate of 6 degrees per minute.

The reason for the above statements are obvious if you think a layer deep. Now, for the code (works both for C++ and Java)


Cheers!!
Jack.

What is the difference between memcpy and memmove?

Answer:

With memcpy, the destination cannot overlap the source at all. With memmove copying takes place as if an intermediate buffer was used, allowing the destination and source to overlap. This means that memmove might be very slightly slower than memcpy, as it cannot make the same assumptions.

Cheers!!
Jack

Linked List : Given a pointer to any node, delete the node pointed by the pointer

Given a linked list like this,

Given a pointer to any node, delete the node pointed by the pointer. Note: no head pointer is given.

Solution:

Assume a pointer to p3, lets call it to 'p'. Since only pointer to current node is provided, there is no way to delete the current node from the list. But instead of deleting the current node, we can just move the next node data to current node and delete the next node. The algorithm can be explained simply as,

Cheers!!
Jack

C program to find fibonacci series using only one variable !!!

Problem:
Generating Fibonacci series using only one variable.

There are many ways to achieve this. I have given three ways to do this in the following methods.

Method #1:
We can have a simple function to do this.

Method #2:
The following recursive function would do the job.

Method #3:
The following one works great as well!

Cheers!!
Jack

Interview Puzzle - Equal heads

Puzzle:

There are 50 coins on the table out of which 43 are tail-face up and 7 are head face up. You are blind folded and there is no way to determine which side is up by rubbing, etc. You have to divide the 50 coins in two sets (not necessarily equal) such that both have equal number of coins with heads face up.

Solution:

Divide the 50 coins into two sets - once set with 43 coins and the other set with 7 coins. Thus, the first set will contain 'x' heads and '43-x' tails and the second set will contain '7-x' heads and 'x' tails. The possibilities can be tabulated as shown in the left table.

Now, flip the coins in the second set, so that both will contain 'x' heads. The result after flipping can be seen on the right table. You can see that both sets have equal number of heads whatever be the distribution.

Cheers!!
Jack

Print a Matrix in diagonal zig zag order

Problem:
Given a square matrix, write a program to print the items in zig zag diagonal order.

Following is an example,

So the output expected for the above example is,

1 -> 2 -> 6 -> 3 -> 7 -> 11 -> 4 -> 8 -> 12 -> 16 -> 5 -> 9 -> 13 -> 17 -> 21 -> 10 -> 14 -> 18 -> 22 -> 15 -> 19 -> 23 -> 20 -> 24 -> 25

Solution:

This program is a bit tricky and is very hard to solve immediately when asked in an interview. People who try to attack problems involving matrices always think they need at least two loops to arrive at the solution. But the surprise here is the problem can be solved in just a single loop with a very simple logic. I have provided the solution in C++ below, you may also try to solve the same in the language of your choice!!


Cheers!!
Jack

A Free game in Java

I wanted to play this game so badly as I use to be very good at it. I was not knowing the proper keyword to find it online. So, what the heck, I went ahead and created one! The front end used was Swing.
The objective of this game is to arrange from numbers 1 through 24 (or depending on the size) in proper order and you have one square free. You can move to that empty sqaure by pressing either of the four arrow keys UP/DOWN/LEFT/RIGHT. All the puzzles formed will have a solution. You can use this code anywhere you want.

If you have Java installed in your browser, you should be able to see the Applet. Just click anywhere inside the applet and start playing using the arrow keys! Have fun!

Screenshot	Applet

Cheers,
Bragaadeesh.

Trie data structure - In C++

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Having had a comprehensive coverage of the TRIE data structure in Java, me and my roommate thought it would achieve completion if we have the same implemented in C++. Don't get carried away by the length of the code. Its as simple and easy as the equivalent one in Java. You may go through the comprehensive tutorial here. Trust me, it takes only 10 minutes!!.

Please feel free to ask any questions if you face difficulties in understanding any part of the resource. I would respond to you immediately.


Demonstration of trie operations

Cheers!!
Jack.

Efficient way to calculate prime numbers

In several puzzles/coding competitions we may need to check for prime numbers and this is required to be done in considerable time to save precious run time. The traditional approach is,



This will however will loop through all elements below x to see if a factor exists. Example, for finding if 13 is prime, we check if its divisible by 2,3,4,....12. This can be optimized to loop through only half the elements since the highest factor is going to be num/2 as,


But by analysis you can see that for a number say 100, the factors are (1*100),(2*50),(4*25),(5*20),(10*10),(20*5),(25*4),(50*2),(100*1). For finding out if 100 is prime or not we just need to check if 100 is divisible by any number not greater than 10 i.e., it is sufficient to check from 2 to 10. The reason being if its divisible by 4, its also divisible by 25.

Hence the best approach to check if a number is prime or not will be



Final prime number program in Ruby (bonus)


This approach will check for factors in very minimized number of loops.

Cheers!!
Bragaadeesh