排列算法

package org.example.permandcombine;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * @author xianzhe.ma
 * @date 2021/11/3
 */

public class Permutation {

    public static ArrayList<String> Permutation(String str) {
        int length = str.length();
        List<String> inputList = new ArrayList<>();
        for (int i = 0;i<length;i++) {
            char c = str.charAt(i);
            String temp = String.valueOf(c);
            inputList.add(temp);
        }

        String[] array = new String[length];
        inputList.toArray(array);

        ArrayList<String> result = new ArrayList<>();

        doPerm(array, 0, length, result);
        Set<String> set = new HashSet<>();
        set.addAll(result);

        ArrayList<String> result2 = new ArrayList<>();
        result2.addAll(set);
        return result2;

    }

    public static void main (String[] args) {
        String str = "ABC";

        ArrayList<String> list = Permutation(str);
        for (String str1 : list) {
            System.out.println(str1);
        }
    }

    public static void doPerm(String[] array, int start, int end, ArrayList<String> result) {

        if (start == end) {
            int size = array.length;
            StringBuilder stringBuilder = new StringBuilder();
            for (int i=0;i<size;i++) {
                stringBuilder.append(array[i]);
            }

            result.add(stringBuilder.toString());
            return;
        }

        for (int i= start;i<end;i++) {
            swap(array, start, i);
            doPerm(array,start+1,end, result);
            swap(array, start, i);
        }

    }

    public static void swap(String[] array, int i, int j) {
        String temp = array[i];
        array[i] = array[j];
        array[j] = temp;
    }
}