Problem on Bit Manipulation

Write a function to determine the number of bits required to convert integer X to integer Y.
Input: 31, 14
Output: 2


This problem seems to be quite complex, however is actually rather simple. Think about finding out which bits in two numbers are different. Simple: with an XOR.
Each 1 in the XOR will represent one different bit between X and Y. Then we can simply count the number of bits that are 1.

 public static int swapRequired(int x, int y)
{
 int counter = 0;
 for (int z = x ^ y; z!= 0; z= z>>1) {
 counter += c & 1;
 }
 return counter;
 }

Reverse a Linked List

This question is one of the most repeated ones across Google, Microsoft, Amazon and a few more. The thing which makes it a good question is that after you scratch your head and give them an algorithm they either ask you to optimize it for the boundary cases (which is fine for most of the candidates) or they ask you to do it the other way round.

I am going to give you both, recursive as well as an iterative solution. For both the techniques :

Initially call the method as : head = reverseList(head,NULL)


Iterative :

Node *Reverse (Node *p)
{
   Node *pr = NULL;
   while (p != NULL)
   {
      Node *tmp = p->next;
      p->next = pr;
      pr = p;
      p = tmp;
   }
   return pr;
}
-----------------------------------------------------------------------
Recursive:

Node *reverseList(Node *current, Node *parent)
{
        Node *revHead;
   if(current == null)
      revHead = parent;
   else
   {
      revHead = reverseList(current->next,current);
      current->next = parent;      
   }
   return revHead;
}

Easy-4

void main()

{

int *mptr, *cptr;

mptr = (int*)malloc(sizeof(int));                               //Output: some garbage values

printf(“%d”,*mptr);

int *cptr = (int*)calloc(sizeof(int),1);                      // Output=0

printf(“%d”,*cptr);

}

The above statements return garbage values and a zero in the next.

So much for understanding a small difference between malloc() and calloc().

See the differences in arguments and the returned values.

A few simple logical questions !

1.) 

Multiplying a number by 7 without using * and + operators.

NewNum = Num << 3;                      // multiplied by 2^3 = 8

NewNum = NewNum - Num;             // 8 – 1 = 7

2.)

Finding the last character of any String.

                              (OR)

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


char *lastChar(char *String, char ch)
{
char *cStr = NULL;


// traverse the entire string


while(*String ++ != NULL ) 
{
if(*String==ch) 
cStr = String;
}
return cStr;
} 

C Output Type Question

main( )
{
static int a[ ] = {0,1,2,3,4};
int *p[ ] = {a,a+1,a+2,a+3,a+4};
int **ptr = p;
ptr++;
printf(“\n %d  %d  %d”, ptr-p, *ptr-a, **ptr);
*ptr++;
printf(“\n %d  %d  %d”, ptr-p, *ptr-a, **ptr);
*++ptr;
printf(“\n %d  %d  %d”, ptr-p, *ptr-a, **ptr);
++*ptr;
printf(“\n %d  %d  %d”, ptr-p, *ptr-a, **ptr);
}

Try to find the output !!
This question is seemingly quite unconventional, but try it out without using a compiler, and then compare your results with:


1 1 1
2 2 2
3 3 3
3 4 4

Acyclic Linked-List Detection Algorithm

Write a function that takes a pointer to the head of a list and determines whether the list is cyclic or acyclic. Your function should return false if the list is acyclic and true if it is cyclic. You may not modify the list in any way.

int determineTermination( node *head )
        { 
           node *fast, *slow;
           fast = slow = head; 
                  while( true )
                       {
                           if( !fast || !fast->next ) 
                              return false; 
                           else if( fast == slow || fast->next == slow ) 
                              return true; 
                           else 
                              {
                                 slow = slow->next; 
                                 fast = fast->next->next; 
                              }
                        }
        }


Leave your comments below the post.
Happy coding :)

Microsoft Moderate Programming Question

An important interview as well as optimised solution for finding the largest sub array sum in an array which may contain 0, positive and negative integers.


#include<stdio.h>
main()
{
int sumtillnow=0,sum=0,i=0;
int a[7]={-1,11,13,12,-90,23,5};
for(i=0;i<7;i++)
{
sumtillnow+=a[i];
if(sumtillnow>sum)
 sum=sumtillnow;
if(sumtillnow<0)
 sumtillnow=0;
 }
printf("%d",sum);
}

One line of code for finding out whether a number is power of 2 or not

(An obnoxious looking piece of code) 

If the following LOC returns true, find out what is x here ?

if((x&&!(x&(x-1))==1)) 

Study the Bit-wise operators well, many problems and contests have questions which become quite easy if these are used !!
 The above code is a simple one line test for testing if a variable entered or passed is a power of 2.

So do you also want to become a good programmer someday ??

It is no secret that every programmer cherishes a dream of hitting the headlines of the for doing something really great. Although there are not many world famous programmers in this world, and the best ones rarely opt for a life in public. In most cases it is because of the nature of the work which forces them to hit their machines harder each passing day.
Believe me its no joke and neither it is a cakewalk to be successful as a programmer, because programming in the first place is not about learning programming languages, instead it is about the machine, logic and semantics. The code is just something which comes on in after the three have been developed. Choice of a particular language is purely something that is your own and u needn't be advised by anyone. Lastly, expecting overnight success just because you completed that Complete Reference or Bible of XYZ language is called stupidity and i pray to God that such people get some brains soon enough. Dear Reader, after reading the book you need to implement the constructs and syntax on your machine and some problems. Open up a few websites and blogs (like this one) and start to think about the solutions to them, and if you have done enough then start optimizing them or finding new methods to solve the same problem.
There are a few really great articles i would like you to refer :

1.  How to be a good programmer.
2.  How to be come a good programmer in.....