【剑指offer】面试题45：把数组排成最小的数

题目

输入一个正整数数组，把数组里所有数字拼接起来排成一个数，打印能拼接出的所有数字中最小的一个。
例如输入数组{3，32，321}，则打印出这三个数字能排成的最小数字为321323。

思路

考虑到两个数字的拼接可能会出现溢出问题，所以该问题使用字符串来处理
可以转换成字符串排序问题
如数字a与数字b，拼接成字符串ab和字符串ba，
然后按照字典序进行比较，如果ab < ba，则数字a应该排在前面，否则反之

代码

public class _45_SortArrayForMinNumber {    public static String PrintMinNumber(int [] numbers) {        if(numbers == null || numbers.length == 0)            return "";        TreeSet<String> set = new TreeSet<>(new Comparator<String>() {            // 不应该出现0的情况            @Override            public int compare(String o1, String o2) {                return (o1 + o2).compareTo(o2 + o1) > 0 ? 1 : -1;            }        });        for(int number : numbers) {            set.add(String.valueOf(number));        }        StringBuilder sb = new StringBuilder();        for(String s : set) {            sb.append(s);        }        return sb.toString();    }}

测试

public class _45_Test {    public static void main(String[] args) {        test1();        test2();        test3();    }    private static void test1() {        String s = _45_SortArrayForMinNumber.PrintMinNumber(new int[] {12, 123, 1});        MyTest.equal(s, "112123");        s = _45_SortArrayForMinNumber.PrintMinNumber(new int[] {43, 3, 134});        MyTest.equal(s, "134343");        s = _45_SortArrayForMinNumber.PrintMinNumber(new int[] {43, 4});        MyTest.equal(s, "434");        s = _45_SortArrayForMinNumber.PrintMinNumber(new int[] {45, 4});        MyTest.equal(s, "445");    }    private static void test2() {        String s = _45_SortArrayForMinNumber.PrintMinNumber(new int[] {4});        MyTest.equal(s, "4");        s = _45_SortArrayForMinNumber.PrintMinNumber(new int[] {1,111,1111});        MyTest.equal(s, "11111111");    }    private static void test3() {        String s = _45_SortArrayForMinNumber.PrintMinNumber(null);        MyTest.equal(s, "");        s = _45_SortArrayForMinNumber.PrintMinNumber(new int[0]);        MyTest.equal(s, "");    }}