c# - Generate random numbers without repetitions

How to generate Random numbers without repeating any numbers in the given target like(1-5000) there should be no reparation and I should be able to get 5000 randomized numbers. I should be able to run the randomized as many times as the user wants,How to do with C#

For Sample Target is (1-10) No of times to run =2

First run: 5,4,6,8,3,1,2,0,7,10

second run 6,3,5,8,4,2,0,1,10,7

Like this I should be able to get the results as many times as I run..

Answer

As others have pointed out, what you're looking for is effectively a shuffled deck of cards. Every card (in this case, a unique number) is present exactly once, in a randomized order. By drawing cards from the deck one at a time, you create a psuedorandom number string with no repeats.

(Obviously, once you've exhausted the deck, you'll need to either reuse it or reshuffle it to generate the next number)

A fast way to do this is with a Fisher-Yates shuffle, also commonly called a Knuth Shuffle:

// Prepare a deck of sequential numbers from min to max:

int count = max - min + 1
int[] deck = new int[count];

for(int i = 0; i < count; i++)
{
   deck[i] = min + i;
}



// Shuffle it:

for(int i = count - 1; i > 1; i--)
{
    // Pick an entry no later in the deck, or i itself.
    int j = Random.Range(0, i + 1);

    // Swap the order of the two entries.
    int swap = deck[i];

    deck[i] = deck[j];
    deck[j] = swap;
}

// Now deck[] contains all numbers from min to max
// in a random order with no duplicates.

This can also be combined into one pass:

int count = max - min + 1;
int[] deck = new int[count];


for(int i = 0; i < count; i++)
{
    int j = Random.Range(0, i + 1);

    deck[i] = deck[j];
    deck[j] = min + i;
}

One neat trick is that you don't even have to shuffle all at once for this. You can randomize as you go, at a constant cost per card drawn:

[System.Serializable]
public class Deck {
    [SerializeField]
    T[] deck; 

    // Tracks a partition between the deck & discard pile.
    // All entries at i < remaining are in the undrawn deck,
    // remaining <= i < deck.Length are in the discard pile.
    int remaining = 0;


    public T Draw() {
        // If we ran out of cards, shuffle the discards to make a new deck.
        if(remaining == 0)
            remaining = deck.Length;

        // Pick a card at random from the remaining deck.
        int chosenIndex = Random.Range(0, remaining);
        T chosenItem = deck[chosenIndex];

        // Remove the card from the remaining deck and place it at the

        // top of the growing discard pile.
        remaining--;
        deck[chosenIndex] = deck[remaining];
        deck[remaining] = chosenItem;

        return chosenItem;
    }
}