UVa 713. Adding Reversed Numbers

UVa 713: Adding Reversed Numbers is a straight-forward problem that can be solved using an ad-hoc algorithm. We have discussed a similar problem in a previous blog-post. However, this problem imposes following additional constraint—numbers will be at most 200 characters long–which necessitates the use of BigInteger. Following Java code shows such an ad-hoc algorithm that solves this problem by considering the stated constraints.

import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.Scanner;
class Main {
private final Scanner in;
private final PrintWriter out;
public Main(){
in = new Scanner(System.in);
out = new PrintWriter(System.out, true);
public Main(Scanner in, PrintWriter out){
this.in = in;
this.out = out;
private static BigInteger bigIntAfterRemovingTrailingZeros(String num){
int nonZeroIndex=num.length()-1;
for (; nonZeroIndex>=0; nonZeroIndex--){
if (num.charAt(nonZeroIndex) != '0'){
return new BigInteger(num.substring(0, nonZeroIndex+1));
private static BigInteger[] readLineAsBigInts(String input){
String [] ints = input.trim().split(" ");
BigInteger [] rets = new BigInteger[2];
rets[0] = bigIntAfterRemovingTrailingZeros(ints[0]);
rets[1] = bigIntAfterRemovingTrailingZeros(ints[1]);
return rets;
private static BigInteger reversedBigInt(BigInteger num1){
BigInteger reversedNum = BigInteger.ZERO;
final int _REM = 1;
final int _QUOTIENT = 0;
while (num1.compareTo(BigInteger.ZERO)>0){
BigInteger [] results = num1.divideAndRemainder(BigInteger.TEN);
reversedNum = reversedNum.add(results[_REM]);
reversedNum =reversedNum.multiply(BigInteger.TEN);
num1 = results[_QUOTIENT];
return reversedNum;
private static BigInteger getAddRevNumbers(BigInteger num1, BigInteger num2){
return reversedBigInt(reversedBigInt(num1).add(reversedBigInt(num2)));
public void run(){
final int T = Integer.parseInt(in.nextLine().trim()); // no of test cases
BigInteger [] numbers;
for (int testCase = 0 ; testCase< T ; testCase++){
numbers = readLineAsBigInts(in.nextLine());// read input
out.println(getAddRevNumbers(numbers[0], numbers[1]));// print result
public static void main(String[] args) {
Main uva713Solver = new Main();
view raw uva713.java hosted with ❤ by GitHub

Please leave a comment if you have any question. Thanks.

See Also

see Party Schedule postSPOJ 42. Adding Reversed Numbers (ADDREV) with F#.

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