PickClass.sol

//Classes
//Record Studuent pick.
//Cal Result 
//Studuent Pick Class(Not Pick)
//Pick End Time.
//Query Time 

pragma solidity ^0.4.8;
import "https://github.com/OpenZeppelin/zeppelin-solidity/contracts/math/SafeMath.sol";
contract PickClass {
    using SafeMath for uint;
    address[] private pickClassStudents;
    address[] private chosedClassStudents;
    mapping(address => bool) chosed;
    mapping(address => bool) picked;
    address owner;
    uint private classsNumber;
    uint private currentRandomLength;
    uint private chosedRandom;
    uint256 hash;
    
    modifier isValidPick() {
        require(!picked[msg.sender]);
        _;
    }
    
    modifier isOwner() {
        require(msg.sender == owner);
        _;
    }
    
    function PickClass() public {
        owner = msg.sender;
        hash = now;
    }
    
    function mockStudent() isValidPick public {
        //it's for test 
        pickClassStudents.push(0x0);
        pickClassStudents.push(0x1);
        pickClassStudents.push(0x2);
        pickClassStudents.push(0x3);
        pickClassStudents.push(0x4);
        pickClassStudents.push(0x5);
        pickClassStudents.push(0x6);
        pickClassStudents.push(0x7);
        pickClassStudents.push(0x8);
        pickClassStudents.push(0x9);
        pickClassStudents.push(0x10);
        pickClassStudents.push(0x11);
        pickClassStudents.push(0x12);
        pickClassStudents.push(0x13);
        pickClassStudents.push(msg.sender);
    }

    function pickClass() isValidPick public {
        pickClassStudents.push(msg.sender);
        picked[msg.sender] = true;
    }
    
    function chose(uint studentNumber) isOwner public {
        //Random
        currentRandomLength = pickClassStudents.length;
        for(uint i = 0; i < studentNumber; ++i) {
            chosedRandom = random(0, currentRandomLength);
            chosedClassStudents.push(pickClassStudents[chosedRandom]);
            (pickClassStudents[chosedRandom], pickClassStudents[currentRandomLength - 1]) = (pickClassStudents[currentRandomLength - 1], pickClassStudents[chosedRandom]);
            chosed[pickClassStudents[chosedRandom]] = true;
            currentRandomLength = currentRandomLength.sub(1);
            if(currentRandomLength == 0) {
                break;
            }
        }
    }
    
    function isChosed() public view returns(bool) {
        return chosed[msg.sender];
    }
    
    function isChosed(address studentAddress) public view returns(bool) {
        return chosed[studentAddress];
    }
    
    function chosedStudent() public view returns(address[]) {
        return chosedClassStudents;
    }
    
    function pickedStudent() public view returns(address[]) {
        return pickClassStudents;
    }
    
    function random(uint min, uint max) private constant returns(uint) {
        uint random = hash % (max - min) + min;
        hash = uint256(keccak256(hash));
        return random;
    }
}