Question

I have been staring at this code and cannot figure out what is wrong with it, maybe a fresh pair of eyes could help.

public static BigInteger powerOfBigInteger (BigInteger base, BigInteger power){
    if (power == BigInteger.valueOf(0)){
        return BigInteger.valueOf(1);
    }

    if (power == BigInteger.valueOf(1)){
        return base;
    }

    BigInteger x = BigInteger.valueOf(1);
    while (x != power ){
        base.multiply(base);
        x.add(BigInteger.valueOf(1));
        System.out.println(x + " " + power);
                   return base;
    } 

    return base;

I run this and apparently x never equals power. Any help is appreciated.

Answer 1

You should do

if (BigInteger.ZERO.equals(power)) return BigInteger.ONE;
if (BigInteger.ONE.equals(power))  return base;

and you have to accumulate the result of your multiplication and addition because BigInteger is immutable and returns new BigInteger instance

The infinite loop is because your x NEVER changes – should be

x = x.add(BigInteger.ONE);

multiplication should change to

result = result.mulitply(base);

where initial result value should be BigInteger.ONE