28. ERC-721 NFT

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract MyNFT {
    uint256 private _next;
    mapping(uint256 => address) public ownerOf;
    mapping(address => uint256) public balanceOf;
    mapping(uint256 => string) private _uri;
    event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);
    function mint(address to, string memory uri) external returns (uint256) {
        // TODO
    }
    function tokenURI(uint256 id) external view returns (string memory) { return _uri[id]; }
}