Java实现21位水仙花数判断

import java.math.BigInteger;
import java.util.Hashtable;

public class Main {

    private static final int SIZE = 21;
    private int[] countArray = new int[10]; // 个数列表
    private int[] countSumArray = new int[10]; // 个数总数
    private BigInteger[] sumArray = new BigInteger[10];// 值总数
    private int offset = 0;// 浮标

    /**
     * 设置当前浮标对应的个数，个数的总数，值总数
     *
     * @param num
     *            个数
     */
    private void setValue(int num) {
        countArray[offset] = num;
        if (offset == 0) {
            countSumArray[offset] = num;
            sumArray[offset] = p(9 - offset).multiply(n(num));
        } else {
            countSumArray[offset] = countSumArray[offset - 1] + num;
            sumArray[offset] = sumArray[offset - 1].add(p(9 - offset).multiply(n(num)));
        }
    }

    /**
     * 检验当前数据是否匹配

     *
     * @return
     */
    private boolean checkPersentArray() {
        BigInteger minVal = sumArray[offset];// 当前已存在值
        BigInteger maxVal = sumArray[offset].add(p(9 - offset).multiply(n(SIZE - countSumArray[offset])));// 当前已存在值+可能存在的最大值
        // 最小值匹配
        if (minVal.compareTo(MAX) > 0) {
            return false;
        }
        // 最大值匹配
        if (maxVal.compareTo(MIN) < 0) {
            return false;
        }
        String minStr = minVal.compareTo(MIN) > 0 ? minVal.toString() : MIN.toString();
        String maxStr = maxVal.compareTo(MAX) < 0 ? maxVal.toString() : MAX.toString();
        // 找到最小值与最大值间首部相同的部分
        int[] sameCountArray = new int[10];
        for (int i = 0; i < SIZE; i++) {
            char c;
            if ((c = minStr.charAt(i)) == maxStr.charAt(i)) {
                sameCountArray[c - '0'] = sameCountArray[c - '0'] + 1;
            } else {
                break;
            }
        }
        // 判断如果相同部分有数据大于现在已记录的位数，返回false
        for (int i = 0; i <= offset; i++) {
            if (countArray[i] < sameCountArray[9 - i]) {
                return false;