You have an empty sequence, and you will be given queries. Each query is one of these three types: 1 x -Push the element x into the stack.

MaximumElement.java

import java.io.*;
import java.util.*;
import java.util.stream.*;

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

class Result {

    /*
     * Complete the 'getMax' function below.
     *
     * The function is expected to return an INTEGER_ARRAY.
     * The function accepts STRING_ARRAY operations as parameter.
     */

    public static List<Integer> getMax(List<String> operations) {

        List<Integer> stack = new ArrayList<>();
        List<Integer> output = new ArrayList<>();
        int max = Integer.MIN_VALUE;

        for (int i = 0; i < operations.size(); i++) {

            List<Integer> op = Arrays.stream(operations.get(i).split(" "))
                    .map(Integer::valueOf)
                    .collect(Collectors.toList());

            int opCode = op.get(0);

            switch (opCode){
                case 1:
                    stack.add(op.get(1));
                    if(op.get(1)>max)
                        max = op.get(1);
                    break;
                case 2:
                    int removedElement = stack.get(stack.size()-1);
                    stack.remove(stack.size()-1);
                    if(max==removedElement){
                        max = Integer.MIN_VALUE;
                        for(int j=0;j<stack.size();j++){
                            if(stack.get(j)>max)
                                max = stack.get(j);
                        }
                    }
                    break;
                case 3:
                    output.add(max);
                    break;
            }
        }
        return output;
    }

}

public class MaximumElement {
    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 n = Integer.parseInt(bufferedReader.readLine().trim());

        List<String> ops = IntStream.range(0, n).mapToObj(i -> {
            try {
                return bufferedReader.readLine();
            } catch (IOException ex) {
                throw new RuntimeException(ex);
            }
        })
                .collect(toList());

        List<Integer> res = Result.getMax(ops);

        bufferedWriter.write(
                res.stream()
                        .map(Object::toString)
                        .collect(joining("\n"))
                        + "\n"
        );

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