Write a program to Generate all possible permutations of the string "ABCDEF" using C#.

 Since "ABCDEF" has 6 characters, the number of permutations = 6! = 720.

Here’s a C# program to generate and print them:

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        string input = "ABCDEF";
        var results = new List<string>();

        GetPermutations(input.ToCharArray(), 0, results);

        Console.WriteLine($"Total Permutations: {results.Count}");
        foreach (var str in results)
        {
            Console.WriteLine(str);
        }
    }

    static void GetPermutations(char[] arr, int index, List<string> results)
    {
        if (index == arr.Length - 1)
        {
            results.Add(new string(arr));
        }
        else
        {
            for (int i = index; i < arr.Length; i++)
            {
                Swap(ref arr[index], ref arr[i]);
                GetPermutations(arr, index + 1, results);
                Swap(ref arr[index], ref arr[i]); // backtrack
            }
        }
    }

    static void Swap(ref char a, ref char b)
    {
        if (a == b) return;
        char temp = a;
        a = b;
        b = temp;
    }
}

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🔹 How it works:

1. Uses recursion to generate all permutations.

2. Swaps characters, calls recursively, then backtracks to restore the original order.

3. Stores all unique permutations in a List<string>.

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🔹 Sample Output:

Total Permutations: 720
ABCDEF
ABCDE F
ABCDFE
ABCEDF
...
FEDCBA

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👉 This prints all 720 unique permutations of "ABCDEF".