也来写一个吸血鬼数的求法

import java.util.List;
import java.util.LinkedList;

public class VampireNumber {

    public static void find(int start, int end) {
        System.out.println("start: " + start + ", end: " + end);

        int slen = VampireNumber.getIntegerLength(start);
        int elen = VampireNumber.getIntegerLength(end);
        if(slen % 2 != 0) {
            slen++;
        }
        if(elen % 2 == 0) {
            elen++;
        }
        if(slen >= elen) {
            System.out.println("No suitable number exists in this section.");
            return;
        }

        // 根据范围确定下面循环开始和结束的数字
        int begin = (int)Math.pow(10, slen / 2 - 1);
        int finish = (int)Math.pow(10, (elen - 1) / 2);
        System.out.println("begin: " + begin + ", finish: " + finish);

        for(int i = begin; i < finish; i++) {
            for(int j = i; j < finish; j++) {    // 从i开始，避免出现(17, 27)、(27, 17)这样的重复
                // 如果两个数结尾都是0，则继续
                if(i % 10 == 0 && j % 10 == 0) {
                    continue;
                }
                int first = VampireNumber.getIntegerLength(i);
                int second = VampireNumber.getIntegerLength(j);
                if(second > first) {
                    break;
                } else if(second < first) {
                    continue;
                }

                int value = i * j;
                // 检测value是否已溢出
                if(value < 0) {
                    break;
                }
                if(value < start) {
                    continue;
                }
                if(value > end) {
                    break;
                }

                int len = VampireNumber.getIntegerLength(value);
                if(len != first + second) {
                    continue;
                }

                // 将两个乘数的数字放入List
                List<Integer> numList = new LinkedList<Integer>();
                VampireNumber.getNumberList(i, first, numList);
                VampireNumber.getNumberList(j, second, numList);

                boolean isVampireNumber = true;
                // 将乘积的数字和List中存放的乘数的数字进行比较
                while(value != 0) {
                    int current = value % 10;
                    value /= 10;

                    if(!numList.contains(current)) {
                        isVampireNumber = false;
                        break;
                    }
                    numList.remove(new Integer(current));
                }
                // 如果乘积的数字和List中存放的乘数的数字吻合，则是吸血鬼数
                if(isVampireNumber) {
                    System.out.println("A vampire number found: " + i * j + ", (" + i + ", " + j + ").");
                }
            }
        }
    }

    // 将num的各个位的数字放入list
    public static void getNumberList(final int num, int length, List<Integer> list) {
        int copy = num;
        for(int i = 0; i < length; i++) {
            list.add(copy % 10);
            copy /= 10;
        }
    }

    // 取得num的位数
    public static int getIntegerLength(final int num) {
        int len = 0;
        int copy = num;
        if(copy == 0) {
            return ++len;
        }
        while(copy != 0) {
            copy /= 10;
            len++;
        }
        return len;
    }

    public static void main(String[] args) {
        System.out.println("----------- Now start computing... -----------");
        long s = System.currentTimeMillis();
        VampireNumber.find(0, Integer.MAX_VALUE);
        long f = System.currentTimeMillis();
        System.out.println("----- Computing finished, time used: " + (f - s) + " ms. -----");
    }
}