StakingVault.sol

// File: StakingVault.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract StakingVault is Ownable {
    IERC20 public token;
    mapping(address => uint256) public stakes;
    address[] public stakers;

    event Staked(address indexed user, uint256 amount);
    event Withdrawn(address indexed user, uint256 amount);

    constructor(IERC20 _token) {
        token = _token;
    }

    function stake(uint256 amount) external {
        require(amount > 0, "Zero stake");
        if (stakes[msg.sender] == 0) stakers.push(msg.sender);
        stakes[msg.sender] += amount;
        token.transferFrom(msg.sender, address(this), amount);
        emit Staked(msg.sender, amount);
    }

    function withdraw(uint256 amount) external {
        require(stakes[msg.sender] >= amount, "Insufficient");
        stakes[msg.sender] -= amount;
        token.transfer(msg.sender, amount);
        emit Withdrawn(msg.sender, amount);
    }

    function getTopStakers() public view returns (address[5] memory top) {
        uint256 len = stakers.length;
        address[] memory arr = stakers;
        for (uint i = 0; i < len; i++) {
            for (uint j = i + 1; j < len; j++) {
                if (stakes[arr[j]] > stakes[arr[i]]) {
                    (arr[i], arr[j]) = (arr[j], arr[i]);
                }
            }
        }
        for (uint i = 0; i < 5 && i < len; i++) {
            top[i] = arr[i];
        }
    }
}