How to get Nth Power of any number

Question

I faced an interview. where I was asked the following question

Write a function in any of programming language that computes the nth power of a number w/o using + * or ^ or declaring a new variable inside the function or using any library function (eg Math lib in java).

I have used pow function of java Math.pow(a, b)

Thanks

May I know the reason of -ve voting? is it that you donot know want to help programmers? — Sunil Kumar Sahoo, Jul 06 '11 at 06:16
@Deepak Kumar Sahoo, perhaps because you posted a (homework) assignment without showing any effort of your own. Just a guess. — Bart Kiers, Jul 06 '11 at 06:33
In FORTRAN: `I ** J` ... it doesn't use the `^` operator :-) — Stephen C, Jul 06 '11 at 06:33

score 3 · Answer 1 · answered Jul 06 '11 at 06:44

They're asking whether you understand recursion. Considering x ^ k for some integer k,

when k < 0, x^k = x^k+1 / x
when k = 0, x^k = 1
when k > 0, x^k = x^k-1 * x

Turning this into code shouldn't be too bad. Let's use multiplication for now, and take it out later.

double recursivePower(double x, int k) {
    if (k < 0) {
        return power(x, ++k) / x;
    } else if (k == 0) {
        return 1;
    } else {
        return power(x, --k) * x;
    }
}

Now, to get rid of the multiplication. Since n * m = n / (1/m), we can rewrite the last calculation as power(x, --k) / (1/x):

double recursivePower(double x, int k) {
    if (k < 0) {
        return recursivePower(x, ++k) / x;
    } else if (k == 0) {
        return 1;
    } else {
        return recursivePower(x, --k) / (1 / x);
    }
}

Fractional exponents could probably be done in the same style. If they want irrational exponents to be handled in the same way, I'd ask for Google and a fair amount of time to think about the problem.

score 0 · Answer 2 · answered Jul 06 '11 at 06:13

0

static public int power(int value, int pow){
    if(pow == 0) return 1;

    return value * power(value, pow -1);
}

answered Jul 06 '11 at 06:13

Dapeng

1,704
13
25

score 0 · Answer 3 · answered Jul 06 '11 at 06:28

Done in JavaScript:

function power(num,pow){
  if (pow == 0) return 1
  num /= 1/(power(num,--pow))
  return num
}

Call it like:

power(2,0) // -> 1
power(5,2) // -> 25
power(7,3) // -> 343

I feel like inverse division is cheating the no * operator rule, but eh, maybe that's what they were looking for.

Sunil Kumar Sahoo · Accepted Answer · 2011-07-06T07:07:10.813

-2

I am using java programming language. The interviewer restricted you to declare a new variable inside the method better you pass it to the function. The interviewer didnt restrict you to use division operator (/) so you can use that.

static double getNthPowerOfNumber(double originalNumber,
        int power) {


    if (power == 0) {
        return 1;
    }
    if (originalNumber == 0) {
        return 0;
    } else {
        originalNumber/=1/getNthPowerOfNumber(originalNumber, --power);

        return originalNumber;
    }



}

if you want to get 5th power of a number 3 then write System.out.println("4..double..." + getNthPowerOfNumber(4, 1));

edited Jul 06 '11 at 07:07

answered Jul 06 '11 at 06:06

Sunil Kumar Sahoo

53,011
55
178
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May I know the reason of -ve voting? Donot hide yourself after -ve voting. try to write the reason of -ve voting – Sunil Kumar Sahoo Jul 06 '11 at 06:20
This defines a new variable -- `int i`. – GargantuChet Jul 06 '11 at 06:21
I didn't down-vote, but this solution doesn't work. `1 / originalNumber` is zero. Integer arithmetic. – Stephen C Jul 06 '11 at 06:29
@Stephen, thanks for your reply. check my edited answer. it may work for you. and let me know if it does not work for you – Sunil Kumar Sahoo Jul 06 '11 at 06:58
I think you're gaming for points here. I mean its NOT coincidental at all that you both have the same middle and last name AT ALL. – Jesus Ramos Jul 06 '11 at 07:50
@Jesus, search in stack overflow you will get lots of people with the same middle name and surname. I am working in a company in the mean while I am trying to help others by posting answers in stackoverflow and also i aks questions here. I am not sitting ideal. What is the benefit that that I will get to gain point. I am not employer of stack-overflow. neither i am getting revenue from this. – Sunil Kumar Sahoo Jul 06 '11 at 08:30
@I found alot of persons with your firname also with your last name. I think you donot have all those stackoverflow accounts. How all these persons have similar name like ur? – Sunil Kumar Sahoo Jul 06 '11 at 08:36
nope im the only Jesus Ramos on SO nice defence though. – Jesus Ramos Jul 06 '11 at 08:38
also all of your friends questions are asked by him and answered by you or the other way around even if your answers are downvoted so tell me im wrong? – Jesus Ramos Jul 06 '11 at 08:40
@JesusRamos let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/1176/discussion-between-sunil-kumar-sahoo-and-jesus-ramos) – Sunil Kumar Sahoo Jul 06 '11 at 09:20
yes all programmers are my friends. so i always give answers to any of questions if i can solve. – Sunil Kumar Sahoo Jul 06 '11 at 10:35

How to get Nth Power of any number

4 Answers4