using System;

public class PermGenerator {

​

    static int Fact( int n ) {

        int i = 1;

        while ( n > 0 )

            i *= n--;

        return i;

    }

​

    static void Swap( int[] arr, int n, int m ) {

        int temp = arr[n];

        arr[n] = arr[m];

        arr[m] = temp;

    }

​

    static void GenPerms( int n ) {

        int l, r, fac = Fact(n);  // fac is n! DUH!

        int[] arr = new int[n];

​

        for ( int i = 0; i < n; i++ )

            arr[i] = i + 1;  //  [1, 2, ..., n-1, n]

​

        Console.WriteLine("[" + String.Join(",", arr) + "]");  // initial value

​

        n = n - 1;  // necessary to index zero-based array properly

​

        for ( int i = 2; i < fac; i++ ) {

            l = n - 1;

            r = n;

            while ( arr[l] > arr[r] ) {

                l = l - 1;

                r = r - 1;

            }

​

            r = n;

​

            while ( arr[l] > arr[r] )

                r = r - 1;

​

            Swap( arr, l, r );

            l = l + 1;

            r = n;

​

            while ( l < r ) {

                Swap( arr, l, r );

                l = l + 1;

                r = r - 1;

            }

            Console.WriteLine("[" + String.Join(",", arr) +"]");

        }

        Swap(arr, n, n - 1);  // swap final two elements to complete the series

        Console.WriteLine("[" + String.Join(",", arr) + "]");

    }

​

    public static void Main( string[] args ) {

        int perms = 4;

        PermGenerator.GenPerms(perms);

    }

}