Java solution to Project Euler Problem 16

Problem 16:

2^15 = 32768 and the sum of its digits is 3 + 2 + 7 + 6 + 8 = 26.

What is the sum of the digits of the number 2^1000?

Running time: 5ms

Assessment: Easy and fast using arbitrary-precision arithmetic.

4 thoughts on “Java solution to Project Euler Problem 16

  1. I took some of what you did and optimized it a bit, 4ms for me! haha

    import java.math.BigInteger;
    public class problem16 {
        public static void main(String[]args){
            long begin = System.currentTimeMillis();
            BigInteger x = BigInteger.valueOf(2);
            BigInteger sum = BigInteger.valueOf(0);
            BigInteger dig = BigInteger.valueOf(0);
            BigInteger div = BigInteger.valueOf(10);
            x = x.pow(1000);
            String s2 = String.valueOf(x);
            for(int i=0;i<=s2.length();i++){
                dig=x.remainder(div);
                sum=sum.add(dig);
                x=x.divide(div);
            }
            System.out.println(sum);
            long end = System.currentTimeMillis();
            System.out.println(end – begin + "ms");
        }
    }

  2. public class Prob16 {

    public static void main(String[] args) {

    long begin = System.currentTimeMillis();

    long ans=0;
    char a[]= new char [1000];
    BigInteger two= new BigInteger(“2”);

    a= two.pow(1000).toString().toCharArray();

    for(int i=0;i<a.length;i++)
    {
    ans+= a[i]-'0';
    }

    System.out.println(ans);
    long end = System.currentTimeMillis();
    System.out.println(end – begin + "ms");

    }

    }
    0ms for me :P :P

  3. Good One! The only thing I used from this code is digitToStr = String.valueOf(digit)… So,

    import java.lang.Math;
    import java.math.BigInteger;
    public class PowerDigitSum
    {
    public static void main(String [] args)
    {
    char let;
    String digitToStr = “”;
    int sum = 0, len =0, getInt = 0;
    BigInteger digit = BigInteger.valueOf(2);
    digit = digit.pow(1000);
    digitToStr = String.valueOf(digit);
    len = digitToStr.length();
    for (int i = 0; i<len; i++)
    {
    let = digitToStr.charAt(i);
    getInt = let – 48;//easy way to convert from char to int
    sum +=getInt;
    }
    System.out.println("The digit: " + digit);
    System.out.println("The sum of the digits: " + sum);
    }
    }

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