21位水仙花数

package com.wang;


import java.math.BigInteger;


public class Demo11 {
private static BigInteger[] base = new BigInteger[10];
public static void main(String[] args) {
for(int i=0;i<base.length;i++)
{
base[i] = cal_21(i);
}
int[] a = new int[10];
f(a,0,21);


}

public static BigInteger cal_21(int n)
{
BigInteger b = BigInteger.ONE;
for(int i=0;i<21;i++)
{
b=b.multiply(BigInteger.valueOf(n));
}
return b;

}

public static void f(int[] a,int k,int sum)
{
if(sum == 0)
{
test(a);
return;
}
if(k==a.length-1)
{
a[k] = sum;
f(a,k+1,0);
return;
}
for(int i=0;i<=sum;i++)
{
a[k] = i;
f(a,k+1,sum-i);
a[k] = 0;
}
}

public static void test(int[] a)
{
BigInteger bn = BigInteger.ZERO;
for(int i=0;i<a.length;i++)
{
bn = bn.add(base[i].multiply(BigInteger.valueOf(a[i])));
}
String s = bn.toString();
if(s.length() != 21)
{
return;
}
int[] b = new int[10];
for(int i=0;i<s.length();i++)
{
b[s.charAt(i)-'0']++;
}
for(int i=0;i<10;i++)
{
if(a[i] != b[i])
{
return;
}
}
System.out.println(s);
}


}