【剑指offer】面试题45：把数组排成最小的数

悠悠 2022-06-10 05:25 106阅读 0赞

## 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, "");
        }
    
    }