FatimaO2

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

namespace ConsoleApplication7
{
    class Program
    {
            static void Main(string[] args)
{
    string str = "ABC";
    char[] charArry = str.ToCharArray();
    permute(charArry, 0, 2);
    Console.ReadKey();
}

static void permute(char[] arry, int i, int n)
{
    int j;
    if (i==n)
        Console.WriteLine(arry);
    else
    {
        for(j = i; j <=n; j++)
        {
            swap(ref arry[i],ref arry[j]);
            permute(arry,i+1,n);
            swap(ref arry[i], ref arry[j]); //backtrack
        }
    }
}

static void swap(ref char a, ref char b)
{
    char tmp;
    tmp = a;
    a=b;
    b = tmp;
}
        }
    }