cardguess.sol

pragma solidity ^0.4.18;
contract CardGuess {
    address guesser = 0x0;
    uint256 unlockblock = 0;
    uint256 window = 10;
    bytes32 public hash = 0x28c6468c5e6cd0cd9dac3b0cdfe6c9fde6593813f4a83628fa81f7099b4cf4e9;
    function commit () public {
        require(unlockblock < block.number);
        guesser = msg.sender;
        unlockblock = block.number + window;
    }
    function guess (string solution) public {
        require(guesser == msg.sender);
        require(keccak256(solution) == hash);
        msg.sender.transfer(this.balance);
    }
}