Solidity Contract for Hackathon.

Contest.sol

pragma solidity ^0.4.0;

contract Contest{
    
    struct Participant {
        string email;
        address account;
        bool participated;
    }
    
    Participant[] participants;

    address[] public participantsAccts;
    
    string public company_name;
    uint public prize_amount = 0; // need to change it to accept the float 
    uint public expiry_time;
    address public creator;
    
    address public beneficiary;
    
    bool public ended = false;
    
    function Contest(string _company_name, uint _expiry_time) public {
        
        require(now <= _expiry_time);
        
        creator = msg.sender;
        beneficiary = msg.sender;
        company_name = _company_name;
        expiry_time = _expiry_time;
    }
    
    // get money from creator and add it to the global wallet.
    function load_wallet() public payable {
        
        // only owner of contract can load the wallet
        require(msg.sender == creator);
        
        require(msg.value > 0);
        
        prize_amount = msg.value;
    }
    
    // adding the particant to the array
    function participate(string _email) public {

        // require(!ended);
        
        require(msg.sender != creator);
        
        // TODO: every participant can participate only once
        
        participants.push(Participant({
            email: _email,
            account: msg.sender,
            participated: true
        })); 
        
        participantsAccts.push(msg.sender) -1;
    }
    
    function end() public {

        // require(!ended);

        beneficiary = choose_winner();
        transfer_money(beneficiary);
    }

    // randomly picking a winner and calling the function `transfer_money`
    function choose_winner() public view returns (address) {
        
        require(!ended);
        
        // TODO: if expiry is greater than now
        // require(expiry_time < now);
       
        require(participants.length != 0);
        
        uint total_participant = participants.length;
        uint random_winner_index = uint(block.blockhash(block.number-1))%total_participant;
        address winner = participants[random_winner_index].account;
        
        ended = true;
        
        return winner;
    }   

    // transfer the money from the wallet to either the winner(participant) or the creeator conditionally
    function transfer_money(address winner_account) public {

        require(!ended);
        
        require(msg.sender == creator);

        winner_account.transfer(prize_amount-1);
    }
    
    // to get all the participants
    function get_participants() view public returns (address[]) {
        return participantsAccts;
    }
    
    function kill() public {
        require(msg.sender == creator);
        selfdestruct(creator);
    }
    
}