Programming Puzzle

[Jatinder]

I found these questions on a web site and wish to share with all of u
out there,Can SomeOne Solve these Porgramming puzzles.
Programming Puzzles

Some companies certainly ask for these things. Specially Microsoft.
Here are my favorite puzzles. Don't send me emails asking for the
solutions.

Q1 Write a "Hello World" program in 'C' without using a semicolon.
Q2 Write a C++ program without using any loop (if, for, while etc) to
print numbers from 1 to 100 and 100 to 1;
Q3 C/C++ : Exchange two numbers without using a temporary variable.
Q4 C/C++ : Find if the given number is a power of 2.
Q5 C/C++ : Multiply x by 7 without using multiplication (*) operator.
Q6 C/C++ : Write a function in different ways that will return f(7) =
4 and f(4) = 7
Q7 Remove duplicates in array
Q8 Finding if there is any loop inside linked list.
Q9 Remove duplicates in an no key access database without using an
array
Q10 Write a program whose printed output is an exact copy of the
source. Needless to say, merely echoing the actual source file is not
allowed.
Q11 From a 'pool' of numbers (four '1's, four '2's .... four '6's),
each player selects a number and adds it to the total. Once a number
is used, it must be removed from the pool. The winner is the person
whose number makes the total equal 31 exactly.
Q12 Swap two numbers without using a third variable.
Given an array (group) of numbers write all the possible sub groups of
this group.
Q14 Convert (integer) number in binary without loops.

Q3,12 are similar , Q7 is simple & I know there answer For the Rest
please Help
Wiating for reply.

[Siemel Naran]

"Jerry Coffin" <jc*****@taeus. com> wrote in message
news:b2******** *************** **@posting.goog le.com...

Almost anything you'd normally do with iteration can also be done with
tail recursion.
What is "tail" recursion? Are there other types of recursion?

Any the question says not to use loops. But to me, recursion is a loop,
just expressed differently.

Q5 C/C++ : Multiply x by 7 without using multiplication (*) operator.

One is to just add x together 7 times. Those of us who remember
writing multiplication routines for old processors that didn't have
multiply instructions can easily reduce that to (x<<2)|(x<<1)|x .
Those who've studied Booth's algorithm might try (x<<3)-x, though
without extra bits for the intermediate value, this can overflow.

Are these methods faster than x*7 on modern processors?

Q6 C/C++ : Write a function in different ways that will return f(7) =
4 and f(4) = 7 If you want to get clever with boolean values, you could try:

int f(int x) {
return (x==7*4)+(x==4* 7);
}
Huh?
I'm sure there are more variations as well.

Probably something with mod or %.
Q7 Remove duplicates in array

You can't really "remove" an element from an array, so this is poorly
defined. If it was a C++ vector (for example) std::sort and
std::unique would render it trivial, as would inserting the elements
into an std::set, and then copying them back out. Doing it quickly
while retaining the original order is a little more challenging.

The sort method is O(N*lg(N)) + O(N) if we use comparison sort. But doing
it in place without changing the order seems to be an O(N^2) algorithm, with
the outer loop i running from [0, N) and the inner loop j running from [0,
i). (Seems most people run the inner loop from [i+1, N) and then they run
into problems of how to detect if you've not seen the element already.)

Q8 Finding if there is any loop inside linked list.

One obvious way would be to create a set of pointers to nodes. Walk
the list, inserting each node's address into the set. Quit when you
reach a node with next == NULL (there's no loop) or a node whose
address is already in the set (there's a loop).

There's an alternative that saves memory, but basically destroys the
list if it does contain a loop: as you walk the list, modify each
'next' pointer to point at the previous node. Eventually, you'll
reach either a node with next==NULL, in which case there's no loop, or
else you'll get back to the original head of the list (in which case
there's a loop, and you've wreaked havoc on your list). If the list
doesn't contain a loop, you can re-walk it, again reversing each
pointer, to restore the original list.

Better yet, just ensure the list is constructed sanely, and you'll
know the answer up-front.

There's another. Have two iterators, first one pointing to first element,
the second pointing to the second. The second one is the fast iterator and
you increment it twice in each iteration. The first iterator is the slow
iterator and you increment it once in each iteration. If the list is not
circular the fast iterator will hit NULL at some point. If the list is
circular the fast iterator will equal to the slow iterator at some point.

[Joona I Palaste]

Siemel Naran <Si*********@re move.att.net> scribbled the following
on comp.lang.c:

"Jerry Coffin" <jc*****@taeus. com> wrote in message
news:b2******** *************** **@posting.goog le.com...

Almost anything you'd normally do with iteration can also be done with
tail recursion.

What is "tail" recursion? Are there other types of recursion?
Tail recursion is first doing the computation, then recursing. Head
recursion is the other way around.
Any the question says not to use loops. But to me, recursion is a loop,
just expressed differently.
They're clearly different concepts. At least in C, recursion has a
separate local scope for all levels, while looping reuses the same
local scope for all iterations.

> Q6 C/C++ : Write a function in different ways that will return f(7) =
> 4 and f(4) = 7

If you want to get clever with boolean values, you could try:

int f(int x) {
return (x==7*4)+(x==4* 7);
}

Huh?

In C, the == operator returns 1 if the operands match or 0 if they
don't. Go from there.

--
/-- Joona Palaste (pa*****@cc.hel sinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"The day Microsoft makes something that doesn't suck is probably the day they
start making vacuum cleaners."
- Ernst Jan Plugge

[Irrwahn Grausewitz]

"Siemel Naran" <Si*********@RE MOVE.att.net> wrote:

"Jerry Coffin" <jc*****@taeus. com> wrote in message
news:b2******* *************** ***@posting.goo gle.com...

<snip>

> Q5 C/C++ : Multiply x by 7 without using multiplication (*) operator.

<snip> If you want to get clever with boolean values, you could try:

int f(int x) {
return (x==7*4)+(x==4* 7);
}

Huh?

I'm pretty sure Jerry meant to write:

return (x==7)*4 + (x==4)*7;

Regards
--
Irrwahn Grausewitz (ir*******@free net.de)
welcome to clc: http://www.ungerhu.com/jxh/clc.welcome.txt
clc faq-list : http://www.faqs.org/faqs/C-faq/faq/
clc OT guide : http://benpfaff.org/writings/clc/off-topic.html

[Irrwahn Grausewitz]

Joona I Palaste <pa*****@cc.hel sinki.fi> wrote:

Siemel Naran <Si*********@re move.att.net> scribbled the following
on comp.lang.c:

"Jerry Coffin" <jc*****@taeus. com> wrote in message
news:b2******** *************** **@posting.goog le.com...

> Q6 C/C++ : Write a function in different ways that will return f(7) =
> 4 and f(4) = 7 If you want to get clever with boolean values, you could try:

int f(int x) {
return (x==7*4)+(x==4* 7);
}

Huh?

In C, the == operator returns 1 if the operands match or 0 if they
don't. Go from there.

Now f returns 2 if x equals 28, or 0 otherwise. Great solution. ;-)

Regards
--
Irrwahn Grausewitz (ir*******@free net.de)
welcome to clc: http://www.ungerhu.com/jxh/clc.welcome.txt
clc faq-list : http://www.faqs.org/faqs/C-faq/faq/
clc OT guide : http://benpfaff.org/writings/clc/off-topic.html

[Joona I Palaste]

Irrwahn Grausewitz <ir*******@free net.de> scribbled the following
on comp.lang.c:

"Siemel Naran" <Si*********@RE MOVE.att.net> wrote:

"Jerry Coffin" <jc*****@taeus. com> wrote in message
news:b2****** *************** ****@posting.go ogle.com... <snip>

> Q5 C/C++ : Multiply x by 7 without using multiplication (*) operator. <snip> If you want to get clever with boolean values, you could try:

int f(int x) {
return (x==7*4)+(x==4* 7);
}

Huh?

I'm pretty sure Jerry meant to write: return (x==7)*4 + (x==4)*7;

Dang! I didn't spot that in my original reply. Jerry's original code is
equivalent to return (x==28)+(x==28) , which will return 2 if x==28 but
0 if not.

--
/-- Joona Palaste (pa*****@cc.hel sinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"You can pick your friends, you can pick your nose, but you can't pick your
relatives."
- MAD Magazine

[Joona I Palaste]

Irrwahn Grausewitz <ir*******@free net.de> scribbled the following
on comp.lang.c:

Joona I Palaste <pa*****@cc.hel sinki.fi> wrote:

Siemel Naran <Si*********@re move.att.net> scribbled the following
on comp.lang.c:

"Jerry Coffin" <jc*****@taeus. com> wrote in message
news:b2******** *************** **@posting.goog le.com...
> Q6 C/C++ : Write a function in different ways that will return f(7) =
> 4 and f(4) = 7

If you want to get clever with boolean values, you could try:

int f(int x) {
return (x==7*4)+(x==4* 7);
}

Huh?

In C, the == operator returns 1 if the operands match or 0 if they
don't. Go from there.

Now f returns 2 if x equals 28, or 0 otherwise. Great solution. ;-)

Yes, I noticed it myself later, as you can see. In my defense, it was
Jerry who wrote the incorrect code, I just failed to correct it... =)

--
/-- Joona Palaste (pa*****@cc.hel sinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"And according to Occam's Toothbrush, we only need to optimise the most frequent
instructions."
- Teemu Kerola

[Prawit Chaivong]

js*******@sanch arnet.in (Jatinder) wrote in message news:<22******* *************** ****@posting.go ogle.com>...

I found these questions on a web site and wish to share with all of u
out there,Can SomeOne Solve these Porgramming puzzles.
Programming Puzzles

Some companies certainly ask for these things. Specially Microsoft.
Here are my favorite puzzles. Don't send me emails asking for the
solutions.

Q1 Write a "Hello World" program in 'C' without using a semicolon.
Q2 Write a C++ program without using any loop (if, for, while etc) to
print numbers from 1 to 100 and 100 to 1;
Q3 C/C++ : Exchange two numbers without using a temporary variable.
Q4 C/C++ : Find if the given number is a power of 2.
Q5 C/C++ : Multiply x by 7 without using multiplication (*) operator.
Q6 C/C++ : Write a function in different ways that will return f(7) =
4 and f(4) = 7
Q7 Remove duplicates in array
Q8 Finding if there is any loop inside linked list.
Q9 Remove duplicates in an no key access database without using an
array
Q10 Write a program whose printed output is an exact copy of the
source. Needless to say, merely echoing the actual source file is not
allowed.
Q11 From a 'pool' of numbers (four '1's, four '2's .... four '6's),
each player selects a number and adds it to the total. Once a number
is used, it must be removed from the pool. The winner is the person
whose number makes the total equal 31 exactly.
Q12 Swap two numbers without using a third variable.
Given an array (group) of numbers write all the possible sub groups of
this group.
Q14 Convert (integer) number in binary without loops.

Q3,12 are similar , Q7 is simple & I know there answer For the Rest
please Help
Wiating for reply.

Q3 & Q12

int main()
{
int a = 10;
int b = 20;

/* Swap here */

a ^= b;
b ^= a;
a ^= b;

/* Show value code */
/* .........
* .........
*/
return 0;
}

Please correct me, if I'm wrong. :-)

[boa]

Jerry Coffin wrote:

js*******@sanch arnet.in (Jatinder) wrote in message news:<22******* *************** ****@posting.go ogle.com>... {snip]

Q6 C/C++ : Write a function in different ways that will return f(7) =
4 and f(4) = 7

[snip]

I'm sure there are more variations as well.

int f(int x)
{
return 11 - x;
}

boa
[snip]

[Ioannis Vranos]

Jatinder wrote:

Q3 C/C++ : Exchange two numbers without using a temporary variable.

Isn't the bitwise solution safe only for unsigned integrals?


Regards,

Ioannis Vranos

[Ioannis Vranos]

Siemel Naran wrote:

Q4 C/C++ : Find if the given number is a power of 2.

Easy with some bitwise arithmetic.

x & (x-1) evaluates to zero if the number is an exact power of 2.

The OP cross posted both in clc++ and clc, and the set of questions
obviously consider C as a subset of C++, a dangerous thing to do but anyway.
However in both cases bitwise operations are guaranteed to be safe only
on unsigned integrals, so the above had better include the remark:
"where x is of unsigned integral type".


Regards,

Ioannis Vranos