UVA - 11743 - Credit Check

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int cases=Integer.parseInt(br.readLine());
        StringBuffer sb=new StringBuffer("");
        for(int i=0;i<cases;i++){
             if(checkSum(br.readLine())){
                 sb.append("Valid\n");
             }else{
                 sb.append("Invalid\n");
             }
        }
        System.out.print(sb);
    }

    static boolean checkSum(String x){
        int sum=0;
        StringBuilder temp=new StringBuilder("");
        for(int i=0;i<x.length();i++){
            if(x.charAt(i)>='0' && x.charAt(i)<='9'){
                temp.append(x.charAt(i));
            }
        }
        StringBuilder str1=new StringBuilder("");
        StringBuilder str2=new StringBuilder("");
        for(int i=0;i<temp.length();i++){
            if(i%2==0){
                str1.append(temp.charAt(i));
            }else{
                str2.append(temp.charAt(i));
            }
        }
        StringBuilder ans=new StringBuilder("");
        for(int i=0;i<str1.length();i++){
            ans.append((int)(str1.charAt(i)-48)*2);
        }
        for(int i=0;i<ans.length();i++){
            sum+=(int)(ans.charAt(i)-48);
        }
        for(int i=0;i<str2.length();i++){
            sum+=(int)(str2.charAt(i)-48);
        }
        if(sum%10==0){
            return true;
        }
        return false;
    }
}