Created using remix-ide: Realtime Ethereum Contract Compiler and Runtime. Load this file by pasting this gists URL or ID at https://remix.ethereum.org/#version=soljson-v0.8.21+commit.d9974bed.js&optimize=false&runs=200&gist=

contracts...Set.sol

// SPDX-License-Identifier: MIT

pragma solidity 0.8.21;

contract Set {
    // holds items
    // can enumerate over objects
    uint256[] public items;

    // holds ids
    mapping(uint256 => uint256) private indexes;

    // insert element in the set
    function insert(uint256 value) public {
        require(!contains(value), "Already containts value");

        // if (indexes[value] == 0) {
        // if (!contains(value)) {
            items.push(value);
            indexes[value] = items.length;
        // }
    }

    // remove element from the set
    function remove(uint256 value) public {
        require(contains(value), "Set does not contain such value");

        // find out the index
        uint256 index = indexes[value];

        // moves last element to the place of the value
        // so there are no free spaces in the array
        uint256 lastValue = items[items.length - 1];
        items[index - 1] = lastValue;
        indexes[lastValue] = index;

        // delete the index
        delete indexes[value];

        // deletes last element and reduces array size
        items.pop();
    }

    // check if the set containts the value
    function contains(uint256 value) public view returns(bool) {
        return indexes[value] != 0;
    }

    // length of the Set
    function length() public view returns(uint256) {
        return items.length;
    }

    // list all items in the Set
    function values() public view returns(uint256[] memory) {
        return items;
    }
}