I read about a question that was given to a programmer in an Oracle Interview. I hope he did not get the job, because he simply posted his question on Stack Overflow, but the question itself, looked like a very interesting one.

How would you divide a number by 3 without using

The question, as given on Stack Overflow.`*`

,`/`

,`+`

,`-`

,`%`

, operators?

Think about this question for a while. Perhaps your favourite programming language has a built in solution. Well, C does, so that would make the job as easy as using `div`

:

The

man page of`div()`

function computes the value numerator/denominator and returns the quotient and remainder in a structure named div_t that contains two integer members (in unspecified order) named quotand rem.`div`

This is, of course, the simplest solution available. If your interviewer is trying to look at your knowledge of the language, this would be a fit solution too. I do hope however, that you won’t meet many interviewers who are looking for solutions like these.

It is more interesting to see what you actually know about algorithms and creative problem solving. That’s why someone else responded with this piece of brilliant code:

#include <stdio.h> #include <stdlib.h> int main() { FILE * fp=fopen("temp.dat","w+b"); int number=12346; int divisor=3; char * buf = calloc(number,1); fwrite(buf,number,1,fp); rewind(fp); int result=fread(buf,divisor,number,fp); printf("%d / %d = %d", number, divisor, result); free(buf); fclose(fp); return 0; }

This actually writes `123456`

bytes to a file, which can be of course, any number you are trying to check. After that, it reads chunks of `3`

bytes each, and returns the amount of times it was able to read a chunk. Therefore, it divides the original number by 3.

Of course, this is a horrible solution, but that’s fine, according to the one who posted the code, because it fits the question.

Let’s look at another creative piece of code:

#include <stdio.h> int main() { int dividend = -42, divisor = 5, quotient, remainder; __asm__ ( "cdq; idivl %%ebx;" : "=a" (quotient), "=d" (remainder) : "a" (dividend), "b" (divisor) : ); printf("%i / %i = %i, remainder: %i\n", dividend, divisor, quotient, remainder); return 0; }

This one is creative enough to use another language into C. He decided to use assembly to solve this problem, because even assembly has division instructions built in.

An even better solution came from someone who suggested to use the Setun computer. This was a computer from Moscow that used a ternary system instead of a binary one. This allows you to do one right shift to divide a number by 3.

Obviously, the answer would be to use left and right bit shifting to replace the `+`

and `-`

operators, of course:

// replaces the + operator int add(int x, int y) { while (x) { int t = (x & y) << 1; y ^= x; x = t; } return y; } int divideby3(int num) { int sum = 0; while (num > 3) { sum = add(num >> 2, sum); num = add(num >> 2, num & 3); } if (num == 3) sum = add(sum, 1); return sum; }

But if that is too complicated for you, and you only need a demo, you can always try this:

if (number == 0) return 0; if (number == 1) return 0; if (number == 2) return 0; if (number == 3) return 1; if (number == 4) return 1; if (number == 5) return 1; if (number == 6) return 2;