https://github.com/HappyFunCorp/Webthereum/blob/master/truffle/contracts/MyPrize.sol

MyPrize.sol

pragma solidity ^0.4.18;

contract MyPrize {
  struct Prize {
    uint id;
    address owner;        // current owner
    bytes10 geohash;      // current unclaimed location
    string metadata;      // probably a URL pointing to the full metadata
    uint placedAt;        // block count when it was placed
  }
  
  mapping (uint => Prize) public prizes;

  // Constructor
  function MyPrize() public {
    for (uint i=1; i <= 10; i++) {
        Prize memory prize = Prize({id: i, owner: msg.sender, geohash: "", metadata: "", placedAt: 0});
        prizes[i] = prize;
    }
  }
  
  function placePrize (uint prizeId, bytes10 geohash, string _metadata) public {
    var prize = prizes[prizeId];
    require (prize.id != 0);
    require (geohash != bytes10(""));
    require (prize.owner == address(0) || msg.sender == prize.owner);
    prize.owner = address(0);
    prize.geohash = geohash;
    prize.metadata = _metadata;
    prize.placedAt = block.number;
  }
  
  function claimPrize (uint prizeId, bytes10 geohash) public {
    var prize = prizes[prizeId];
    require (prize.id != 0);
    require (geohash != bytes10("") && prize.geohash == geohash);
    require (block.number - prize.placedAt > 1000);
    prize.owner = msg.sender;
    prize.geohash = "";
    prize.metadata = "";
    prize.placedAt = 0;
  }
}