Problem 30—Digit fifth powers

题目描述如下：

Surprisingly there are only three numbers that can be written as the sum of fourth powers of their digits:

1634 = 1^4 + 6^4 + 3^4 + 4^4

8208 = 8^4 + 2^4 + 0^4 + 8^4

9474 = 9^4 + 4^4 + 7^4 + 4^4

As 1 = 14 is not a sum it is not included.

The sum of these numbers is 1634 + 8208 + 9474 = 19316.

Find the sum of all the numbers that can be written as the sum of fifth powers of their digits.

public class Problem30
{
public static void main(String[] args)
{
long start = System.currentTimeMillis();
int power = 5;
int sum = 0;
for (int i = 2; i < 1000000; i++)
{
if (isDigit(i, power))
{
System.out.println(i);
sum += i;
}
}
System.err.println("sum = " + sum);
System.err.println("time:" + (System.currentTimeMillis() - start));
}

public static boolean isDigit(int num, int power)
{
int length = 1;
int temp = num;
while (temp / 10 > 0)
{
length++;
temp = temp / 10;
}
int sum = 0;
temp = num;
for (int i = 0; i < length; i++)
{
sum += Math.pow((temp % 10), power);
temp = temp / 10;
}
if (num == sum)
{
return true;
}
return false;
}
}

result

4150

4151

54748

92727

93084

194979

sum = 443839

time:1192