把数组排成最小的数

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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。

第一种思路，就是先求出数组的所有排列，然后求排列中最小的数

import java.util.*;public class Solution {    public static String PrintMinNumber(int [] numbers) {        if (numbers.length == 0) return "";        String[] cas = new String[numbers.length];        for (int i = 0; i < numbers.length; i++) {            cas[i] = String.valueOf(numbers[i]);        }        ArrayList<String> strings = Permutation(cas);        String mmin = Check(strings);        return mmin;    }    private static String Check(ArrayList<String> strings) {        long mmin = Long.MAX_VALUE;        for (int i = 0; i < strings.size(); i++) {            mmin = Math.min(mmin, Long.valueOf(strings.get(i)));        }        return String.valueOf(mmin);    }    public static ArrayList<String> Permutation(String[] str) {        ArrayList<String> list = new ArrayList<>();        if (str == null||str.length == 0) return list;        HashSet<String> set = new HashSet<>();        change(set, 0, str);        list.addAll(set);        Collections.sort(list);        return list;    }    private static void change(HashSet<String> set, int k, String[] chars) {        if (k == chars.length) {            String cas = "";            for (int i = 0; i < chars.length; i++) cas += chars[i];            set.add(cas);            return;        } else {            for (int i = k; i < chars.length; i++) {                swap(chars, k, i);                change(set, k+1, chars);                swap(chars, k, i);            }        }    }    private static void swap(String[] chars, int i, int j) {        if (i != j) {            String tmp = chars[i];            chars[i] = chars[j];            chars[j] = tmp;        }    }}

另一种，制定排序规则

//先将整型数组转换成String数组，然后将String数组排序，最后将排好序的字符串数组拼接出来public class Solution {    public static String PrintMinNumber(int [] numbers) {        if (numbers.length == 0) return "";        String result = "";        ArrayList<Integer> list = new ArrayList<>();        for (int i = 0; i < numbers.length; i++) list.add(numbers[i]);        Collections.sort(list, new Comparator<Integer>() {            @Override            public int compare(Integer o1, Integer o2) {                String s1 = o1+""+o2;                String s2 = o2+""+o1;                return s1.compareTo(s2);            }        });        for (int j:list) {            result += j;        }        return result;    }    //测试    public static void main(String[] args) {        int[] numbers = {3, 32, 321};        System.out.println(PrintMinNumber(numbers));    }}

或

//先将整型数组转换成String数组，然后将String数组排序，最后将排好序的字符串数组拼接出来public class Solution {    public static String PrintMinNumber(int [] numbers) {        if (numbers.length == 0) return "";        String result = "";        String[] str = new String[numbers.length];        for (int i = 0; i < numbers.length; i++) {            str[i] = String.valueOf(numbers[i]);        }        Arrays.sort(str, new Comparator<String>() {            @Override            public int compare(String o1, String o2) {                String s1 = o1+o2;                String s2 = o2+o1;                return s1.compareTo(s2);            }        });        for (int i = 0; i < str.length; i++) {            result += str[i];        }        return result;    }    //测试    public static void main(String[] args) {        int[] numbers = {3, 32, 321};        System.out.println(PrintMinNumber(numbers));    }}

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