What's the best way to randomly distribute a fixed number of NFTs?

NFT
1

Hey everyone! I’m trying to figure out how to randomly mint NFTs with specific quantities. Here’s what I want to do:

  • 200 super rare NFTs
  • 300 rare NFTs
  • 500 common NFTs

The tricky part is I need the minting to be random, so users could get any type, but by the end, we should have exactly those numbers for each category.

I’ve got some code that does the random part, but it doesn’t guarantee the final amounts will match what I want. Any ideas on how to make this work? I’m pretty new to smart contracts, so simple explanations would be awesome!

Here’s a basic example of what I’ve tried:

function mintRandomNFT(address recipient) public {
  require(totalMinted < maxSupply, "All NFTs minted");
  uint256 randomNum = getRandomNumber();
  
  if (randomNum < 200) {
    mintSuperRare(recipient);
  } else if (randomNum < 500) {
    mintRare(recipient);
  } else {
    mintCommon(recipient);
  }
  
  totalMinted++;
}

But this doesn’t ensure I’ll end up with the exact numbers I want. Any suggestions?

2

yo zoe, cool project! have u tried using a weighted randomization? u could assign weights to each type based on their desired quantities, then use a cumulative distribution function to pick randomly. it’d ensure u hit ur target nums while keeping the minting random. just a thought, might be worth lookin into!

3

A robust approach to your NFT distribution challenge would be implementing a reservoir sampling algorithm. This method ensures a random selection while maintaining the exact quantities you specified. Here’s a high-level overview:

  1. Create an array containing all 1000 NFT types in the desired proportions.
  2. Shuffle this array thoroughly at the contract deployment.
  3. For each mint, select the last element of the array and swap it with a random element from the remaining unminted NFTs.
  4. Decrement the array size after each mint.

This technique guarantees randomness and the precise distribution you’re aiming for. It’s also gas-efficient as it doesn’t require complex calculations for each mint. You’d need to adapt this concept to Solidity, but it should solve your distribution problem effectively.

4

hey zoe! that’s a cool project you’re working on :smiley: i’ve been thinking about nft distribution too and your question got me curious. have you considered using a pool system? like, you could create a pool with all 1000 nfts (200 super rare, 300 rare, 500 common) and then randomly draw from that pool each time someone mints. that way, you’re guaranteed to have the exact numbers you want by the end.

but then i wonder, how would you implement that in solidity? maybe an array of all the nft types that you shuffle? or some kind of mapping? :thinking:

also, how are you handling the randomness? i’ve heard that on-chain randomness can be tricky. are you using chainlink vrf or something similar?

btw, love your username! do you actually surf? i’ve always wanted to try it but im scared of sharks lol