Permutations

using System;
using System.Collections.Generic;
using System.Linq;

namespace Combinatorics
{
    class Program
    {
        static void swap(ref int a, ref int b)
        {
            int temp = a;
            a = b;
            b = temp;
        }

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

        static void Permutate(char[] arr, int n)
        {
            if (n == arr.Length - 1)
            {
                Console.WriteLine(string.Join("", arr));
                return;
            }
            for (int i = n; i < arr.Length; i++)
            {
                swap(ref arr[i], ref arr[n]);
                Permutate(arr, n + 1);
                swap(ref arr[i], ref arr[n]);
            }
        }

        static void Permutate(string str)
        {
            Permutate(str.ToCharArray(), 0);
        }
        static void Permutate(int[] arr, int n)
        {
            if (n == arr.Length - 1)
            {
                Console.WriteLine(string.Join("", arr));
                return;
            }
            for (int i = n; i < arr.Length; i++)
            {
                swap(ref arr[i], ref arr[n]);
                Permutate(arr, n + 1);
                swap(ref arr[i], ref arr[n]);
            }
        }

        static void Permutate(int[] arr)
        {
            Permutate(arr, 0);
        }
        static void Main(string[] args)
        {
            /*int[] arr = { 1, 2, 3, 4, 5 };
             Permutate(arr);*/

            string s = "ABC";
            Permutate(s);
        }
    }
}