按字母顺序对 ArrayList 进行排序 [英] Sort ArrayList alphabetically

问题描述

我试图找到一个字符串的所有排列并按字母顺序排序.

I'm trying to find all permutations of a string and sort them alphabetically.

这是我目前所拥有的:

public class permutations {

        public static void main(String args[]) {
            Scanner s = new Scanner(System.in);
            System.out.print("Enter String: ");
            String chars = s.next();
            findPerms("", chars);
        }

        public static void findPerms(String mystr, String chars) {

            List<String> permsList = new ArrayList<String>();

                if (chars.length() <= 1)
                        permsList.add(mystr + chars);
                        //System.out.print(mystr + chars + " ");

                else
                        for (int i = 0; i < chars.length(); i++) {
                            String newString = chars.substring(0, i) + chars.substring(i + 1);
                            findPerms(mystr + chars.charAt(i), newString);
                        }

               Collections.sort(permsList);

               for(int i=0; i<permsList.size(); i++) {
                    System.out.print(permsList.get(i) + " ");
               }
       }
}

如果我输入一个字符串toys"，我得到:

IF I enter a string "toys" I get:

toys tosy tyos tyso tsoy tsyo otys otsy oyts oyst osty osyt ytos ytso yots ysto ysot stoy sto syo soyt syto

toys tosy tyos tyso tsoy tsyo otys otsy oyts oyst osty osyt ytos ytso yots yost ysto ysot stoy styo soty soyt syto syot

我做错了什么.我怎样才能按字母顺序得到它们?谢谢！

What am I doing wrong. How can I get them in alphabetical order? Thanks!

推荐答案

您正在从递归方法中调用排序例程，该方法在字符串完全填充之前查找字符串的所有排列

You're calling your sort routine from within the recursive method that finds all permutations of your String, before it's been fully populated

import java.util.*;

public class permutations {

        public static void main(String args[]) {
            Scanner s = new Scanner(System.in);
            System.out.print("Enter String: ");
            String chars = s.next();
            List<String> myList = new ArrayList<String>();
            findPerms(myList, "", chars);

            Collections.sort(myList);

            for(int i=0; i<myList.size(); i++) {
               System.out.print(myList.get(i) + " ");
            }

        }

        public static void findPerms(List<String> permsList, String mystr, String chars) {

            if (chars.length() <= 1)
                permsList.add(mystr + chars);    
            else
            for (int i = 0; i < chars.length(); i++) {
                String newString = chars.substring(0, i) + chars.substring(i + 1);
                findPerms(permsList, mystr + chars.charAt(i), newString);
            }

       }
}

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