Generate NFT metadata and ensure uniqueness

Q: Generate NFT metadata and ensure uniqueness

This question evaluates understanding of combinatorics, deterministic pseudo-random generation, and efficient enumeration for producing unique NFT metadata, measuring competency in algorithm design, state-space management, and handling large-scale outputs.

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Question

You are implementing an NFT metadata generator. Each NFT is defined by selecting exactly one trait value from each trait category. You must generate a requested number of NFTs, ensure they are unique (no repeated trait combinations), and output JSON metadata.

Input

A single JSON object with:

collectionName (string)
traits : an array of trait categories. Each category is:
- name (string)
- values (array of strings, non-empty)
n (integer): number of NFTs to generate
seed (integer): seed for deterministic pseudo-random generation

Example:

{
  "collectionName": "MyCollection",
  "traits": [
    {"name": "Background", "values": ["Blue", "Red"]},
    {"name": "Eyes", "values": ["Normal", "Laser"]}
  ],
  "n": 3,
  "seed": 42
}

Required behavior

Each generated NFT must have exactly one value for each trait category.
Two NFTs are considered the same if they have the same value for every trait category .
Use seed to make generation deterministic:
- Using the same input must produce the same outputs in the same order.
If n exceeds the number of possible unique combinations, output ERROR .

Output

Output a JSON array of length n. Each element is an object:

name : "<collectionName> #<index>" where index starts at 1
attributes : array of { "trait_type": <categoryName>, "value": <selectedValue> }

Example output element:

{
  "name": "MyCollection #1",
  "attributes": [
    {"trait_type": "Background", "value": "Red"},
    {"trait_type": "Eyes", "value": "Laser"}
  ]
}

Constraints

Up to 10 trait categories.
Each category has up to 200 values.
n can be up to 100,000.

Notes

You must define your own approach for generating unique combinations efficiently (not by repeatedly sampling and retrying until unique).