Created using remix-ide: Realtime Ethereum Contract Compiler and Runtime.

contracts...gashapon.sol

// SPDX-License-Identifier: GPL-3.0

pragma solidity ^0.8.4;

contract Gashapon {
    // struct of rank. count is a maximum size of winners array. winners array stores users from user lists
    struct Rank {
        string name;
        uint count;
        string[] winners;
    }
    
    // user and rank lists
    struct List {
        Rank[] ranks;
        bool created;
    }

    address private owner;
    mapping(string => List) listmap;
    
    constructor() {
        owner = msg.sender;
    }

    function getList(string memory _name) external view returns (List memory){
        List storage list = listmap[_name];
        require(list.created);
        return list;
    }
    
    function randMod(uint _count, uint _nonce) private view returns (uint) {
        return uint(keccak256(abi.encodePacked(block.timestamp, msg.sender, _nonce))) % _count;
    }
    
    function allocateUsers(string[] memory _users, Rank[] memory _ranks, string memory _name) external {

        uint userCount = _users.length;
        uint nonce = 0;

        List storage list = listmap[_name];
        require(!list.created);
        
        for (uint i = 0; i < _ranks.length && userCount > 0; ++i) {
            
            Rank memory thisrank = _ranks[i];
            uint rankCount = thisrank.count < userCount ? thisrank.count : userCount;
            thisrank.winners = new string[](rankCount);
            
            for (uint j = 0; j < rankCount; ++j) {
                
                uint rand = randMod(userCount, nonce++);
                thisrank.winners[j] = _users[rand];
                
                _users[rand] = _users[userCount - 1];
                --userCount;
                
            }

            list.ranks.push(thisrank);

        }

        list.created = true;
        
    }
}