Riddles smart contract

Riddles.sol

pragma solidity ^0.5.0;

contract Owned {
    constructor() public { owner = msg.sender; }
    address payable owner;

    modifier onlyOwner {
        require(
            msg.sender == owner,
            "Only owner can call this function."
        );
        _;
    }
}

contract Riddles is Owned {
    bytes32[] private answerHashes;
    uint256 public answerIndex = 0;

    constructor(bytes32[] memory _answerHashes) public {
        answerHashes = _answerHashes;
    }
    
    function sendAnswer(bytes memory answer) public onlyOwner returns (bool) {
        require(answerIndex < answerHashes.length);
        bytes32 answerHash = sha256(answer);
        if (answerHash == answerHashes[answerIndex]) {
            // right answer
            answerIndex++;
            if (answerIndex == answerHashes.length) {
                // end of the riddle challenge!
                selfdestruct(msg.sender);
            }
            return true;
        } else {
            return false;
        }
    }
}