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contracts...NestedMapping.sol

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.0;

contract NestedMapping {
    struct Employee {
        string name;
        uint256 salary;
    }

    mapping(string => mapping(address => Employee)) private employees;

    function getEmployee(string memory department, address _address) external view returns (Employee memory) {
        Employee memory employee = employees[department][_address];
        require(employee.salary != 0, "Employee does not exist");
        return employee;
    }

    function addEmployee(string memory department, address _address, string memory name, uint256 salary) external {
        require(_address != address(0), "Invalid address");
        require(bytes(name).length > 0, "Name cannot be empty");
        require(employees[department][_address].salary == 0, "Employee already exists");
        
        employees[department][_address] = Employee(name, salary);
    }
}