CODEWITHSUNDEEP
calgorithmbit-manipulation
someone
someone

Reputation: 1694

Find the next number divided by 8?

Hi this is an interview question.

For any given number calculate next number which is divisible by 8.

i.e. If given number is 43, our algorithm should produce 48 as result. If number is already divisible by 8 it should say Number already divisible by 8 and produce next number divisible by 8.

I suggest them that any number which is divisible by 8 have last three bits as 0 (LSB+2,LSB+1,LSB). But I am not able to give exact solution.

What I said is right approach to solve this problem or we can go for some smarter solution? I need to do this with bit manipulation.

Upvotes: 0

Views: 2148

Answers (5)

somesh babu
somesh babu

Reputation: 21

void main()
{
   int n;
   printf("\n Enter the number:");
   scanf("%d",&n);
   if(n==8 && n%8==0)
   printf("%d it is already divisible by 8",n);
   else
   {
      printf("not divsible by 8 so nearest number is:");
      i=n/8;
      i++;
      n=i*8;
      printf("%d is next number divisible by 8",n);         
   }
}

you can try this which is one of the solution

Thankyou.

Upvotes: 0

IVlad
IVlad

Reputation: 43487

It's easy with a while loop:

if number % 8 == 0
  already divisible by 8

while number % 8 != 0
  ++number

This is O(1), since 8 is a constant, but we can do better with the following formula:

if number % 8 == 0
  already divisible by 8

number = number + 8 - number % 8

Upvotes: 2

Ingo
Ingo

Reputation: 36349

You're on the right track.

int next8(int n) {
    int bits = n & 7; // give us the distance to the previous 8
    if (bits == 0) printf("Number already divisible by 8");
    return n + (8-bits);
}

(Note: I hate it when functions that are supposed to be pure print something, but the task demands so. Sorry.)

Upvotes: 9

Vadim
Vadim

Reputation: 2865

Your check is correct, to check it you can perform a bitwise AND with 7 and make sure it is 0 (X & 7 == 0). To get the next number - Shift right by 3, add 1 and shift back ( ((X >> 3) + 1) << 3 )

Upvotes: 0

fjardon
fjardon

Reputation: 7996

next = current + 8 - (current % 8)

Upvotes: 7

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