Batch example scenario

Consider two fields x and y. we have already uploaded or inserted so many  Account records. At that time we haven't written any trigger or we were not aware of the future requirement.

Requirement:  If the x  value is  1  we have to update 10 in DB, if x value is  2 we have to update 20 and so on [code is self-explanatory].  

we might have a huge number of records with these unique values (1,2,3,4) and while processing in DB should be mapped to corresponding values like 20,30,40,50.

As of know, only 4 unique numbers starting from 1. 

for example:
x ---->y
1---->20
2---->30
3---->40
4---->50

Best approach is batch class

global class MapConceptUpdate implements Database.Batchable<sObject>{
    global Database.QueryLocator start(Database.BatchableContext BC)  {
        string query='select id,x_value__c,y_value__c from Account';
        return database.getqueryLocator(query);
    }
    global void execute(Database.BatchableContext BC,List<Account> scope){
        map<double,double> mapval=new map<double,double>();
        mapval.put(1,20);
        mapval.put(2,30);
        mapval.put(3,40);
        mapval.put(4,50);
       
        List<Account> aclist=new List<Account>();
        for(account ac:scope){
            if(ac.x_value__c!=null && !mapval.isEmpty()&& mapval.containsKey(ac.x_value__c)&&mapval.get(ac.x_value__c)!=null){ 
               ac.y_value__c=mapval.get(ac.x_value__c);
               aclist.add(ac);
            }   
        }
        if(!aclist.isEmpty()){
             update aclist; 
        }
       
    }
    
    global void finish(Database.BatchableContext BC) {
        
    }
}