https://tryhackme.com/room/hfb1passcode

RPC_URL=http://10.10.214.203:8545
API_URL=http://10.10.214.203 
PRIVATE_KEY=$(curl -s ${API_URL}/challenge | jq -r ".player_wallet.private_key") 
CONTRACT_ADDRESS=$(curl -s ${API_URL}/challenge | jq -r ".contract_address") 
PLAYER_ADDRESS=$(curl -s ${API_URL}/challenge | jq -r ".player_wallet.address") 
is_solved=`cast call $CONTRACT_ADDRESS "isSolved()(bool)" --rpc-url ${RPC_URL}` 
echo "Check if is solved: $is_solved"

on the API_URL we could see the code

pragma solidity ^0.8.19;

contract Challenge {
    string private secret = "THM{}";
    bool private unlock_flag = false;
    uint256 private code;
    string private hint_text;
    
    constructor(string memory flag, string memory challenge_hint, uint256 challenge_code) {
        secret = flag;
        code = challenge_code;
        hint_text = challenge_hint;
    }
    
    function hint() external view returns (string memory) {
        return hint_text;
    }
    
    function unlock(uint256 input) external returns (bool) {
        if (input == code) {
            unlock_flag = true;
            return true;
        }
        return false;
    }
    
    function isSolved() external view returns (bool) {
        return unlock_flag;
    }
    
    function getFlag() external view returns (string memory) {
        require(unlock_flag, "Challenge not solved yet");
        return secret;
    }
}

Let's try to get the `hint`

cast call $CONTRACT_ADDRESS "hint()(string)" --rpc-url ${RPC_URL}
The code is xxx

convert xxx to the uint256 and run the `unlock`
>xxx = 0x0hhh

cast send $CONTRACT_ADDRESS "unlock(uint256)" 0x0hhh \
  --legacy \
  --gas-price 50gwei \
  --private-key $PRIVATE_KEY \
  --rpc-url $RPC_URL

checking if unlock was successefull

cast call $CONTRACT_ADDRESS "isSolved()(bool)" --rpc-url ${RPC_URL} 
Check if is solved: True

Now we can get the flag

cast call $CONTRACT_ADDRESS "getFlag()(string)" --rpc-url ${RPC_URL}
THM{......}

Done