java 任意花朵数算法

/**
* 花朵数，网友算法下载学习
* @author cxcx
*
*/
public class Arithmetic11 {
private static BigInteger[] table = new BigInteger[10];

public static void main(String[] args) {
long time = System.nanoTime();
find(21);
time = System.nanoTime() - time;
System.out.println(time / 1000000000.0 + "s");
}

public static void find(int n) {
for (int i = 0; i < 10; i++)
table[i] = BigInteger.valueOf(i).pow(n);
int[] nums = new int
;
int index = 0;
int num = 0;
BigInteger sum = BigInteger.ZERO;
BigInteger MIN = BigInteger.TEN.pow(n - 1);
BigInteger MAX = BigInteger.TEN.pow(n).subtract(BigInteger.ONE);
while (true) {
if (index < nums.length && num < 10) {
BigInteger temp = sum.add(table[num]);
if (temp.compareTo(MAX) < 0) {
nums[index] = num;
index++;
sum = temp;
continue;
}
} else if (index >= nums.length && sum.compareTo(MIN) > 0) {
int[] temp = getArray(sum);
if (check(nums, true, temp, false))
System.out.println(sum);
} else if (index <= 0) {
break;
}
index--;
num = nums[index];
sum = sum.subtract(table[num]);
num++;
}
}

public static boolean check(int[] a1, boolean copy1, int[] a2, boolean copy2) {
if (a1.length != a2.length)
return false;
if (copy1)
a1 = a1.clone();
if (copy2)
a2 = a2.clone();
Arrays.sort(a1);
Arrays.sort(a2);
return Arrays.equals(a1, a2);
}

public static int[] getArray(BigInteger big) {
String s = String.valueOf(big);
int length = s.length();
int[] res = new int[length];
for (int i = 0; i < length; i++)
res[i] = s.charAt(i) - '0';
return res;
}
}