using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Admin.NET.Core;
public class UtilGetPermutations
{
    public static HashSet<string> GetPermutations(string str)
    {
        var results = new HashSet<string>();
        Permute(str.ToCharArray(), 0, results);
        return results;
    }

    public static void Permute(char[] chars, int index, HashSet<string> results)
    {
        if (index == chars.Length)
        {
            results.Add(new string(chars));
            return;
        }

        for (int i = index; i < chars.Length; i++)
        {
            Swap(chars, index, i);
            Permute(chars, index + 1, results);
            Swap(chars, index, i); // 还原
        }
    }

    public static void Swap(char[] chars, int i, int j)
    {
        char temp = chars[i];
        chars[i] = chars[j];
        chars[j] = temp;
    }

}