Function to add to OZ ERC721 to make an efficient airdrop

Efficient721Airdrop.sol

contract ERC721 {
 // take OpenZeppelin contract and add this at the end:

        uint256 private _lastTokenId;
	
	// uncomment next line if you need totalSupply
	// uint256 public totalSupply;

	/// @dev be careful this function expects recipients to all be unique and not be address(0)
	function _airdrop(address[] calldata recipients) internal virtual {
		uint256 length = recipients.length;
		uint256 tokenId = _lastTokenId;
		address to;

		for (uint256 i; i < length;) {
                        to = recipients[i];
			unchecked {
				// _airdrop should only be used at the very start of the contract
				// so to should not have any balance
				_balances[to] = 1;
				++tokenId;
				++i;
			}

			_owners[tokenId] = to;
			emit Transfer(address(0), to, tokenId);
		}

		_lastTokenId = tokenId;
              	// uncomment next line if you need totalSupply
                // totalSupply += length;
	}
}