Alexa has two stacks of non-negative integers, stack and stack where index denotes the top of the stack.

GameOfTwoStack.java

import java.io.*;
import java.math.*;
import java.security.*;
import java.text.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.function.*;
import java.util.regex.*;
import java.util.stream.*;

import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.toList;

class GameOfTwoStackResult {

    /*
     * Complete the 'twoStacks' function below.
     *
     * The function is expected to return an INTEGER.
     * The function accepts following parameters:
     *  1. INTEGER maxSum
     *  2. INTEGER_ARRAY a
     *  3. INTEGER_ARRAY b
     */

    public static int twoStacks(int maxSum, List<Integer> a, List<Integer> b) {
        int sum = 0;
        int count = 0;
        int i = 0;
        int j = 0;

        while (i < a.size() && (sum + a.get(i)) <= maxSum) {
            sum += a.get(i);
            i++;
        }
        count = i;
        while (j < b.size() && i >= 0) {
            sum += b.get(j);
            j++;
            while (sum > maxSum && i > 0) {
                i--;
                sum -= a.get(i);
            }
            if (sum <= maxSum && (i + j) > count)
                count = i + j;
        }

        //System.out.println("count "+count);
        return count;
    }

}

public class GameOfTwoStack {
    public static void main(String[] args) throws IOException {
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

        int g = Integer.parseInt(bufferedReader.readLine().trim());

        IntStream.range(0, g).forEach(gItr -> {
            try {
                String[] firstMultipleInput = bufferedReader.readLine().replaceAll("\\s+$", "").split(" ");

                int n = Integer.parseInt(firstMultipleInput[0]);

                int m = Integer.parseInt(firstMultipleInput[1]);

                int maxSum = Integer.parseInt(firstMultipleInput[2]);

                List<Integer> a = Stream.of(bufferedReader.readLine().replaceAll("\\s+$", "").split(" "))
                        .map(Integer::parseInt)
                        .collect(toList());

                List<Integer> b = Stream.of(bufferedReader.readLine().replaceAll("\\s+$", "").split(" "))
                        .map(Integer::parseInt)
                        .collect(toList());

                int result = GameOfTwoStackResult.twoStacks(maxSum, a, b);

                bufferedWriter.write(String.valueOf(result));
                bufferedWriter.newLine();
            } catch (IOException ex) {
                throw new RuntimeException(ex);
            }
        });

        bufferedReader.close();
        bufferedWriter.close();
    }
}