InfixToPostfix

package StackAndQueuesExercise;

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

public class InfixToPostfix {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        String[] tokens = reader.readLine().split(" ");

        ArrayDeque<Character> numbers = new ArrayDeque<>();
        ArrayDeque<Character> operands = new ArrayDeque<>();

        for (int i = 0; i < tokens.length; i++) {
            char symbol = tokens[i].charAt(0);
            if (Character.isDigit(symbol)){
                numbers.offer(symbol);
            } else if (symbol == '('){
                operands.push(symbol);

            } else if (symbol == ')') {
                while (operands.peek() != '('){
                    char current = operands.pop();
                    numbers.offer(current);
                }
                operands.pop();

            } else {
                operands.push(symbol);
            }
        }

        while (!operands.isEmpty()){
            char current = operands.pop();
            numbers.offer(current);
        }

        while (!numbers.isEmpty()){
            System.out.print(numbers.poll() + " ");
        }
    }
}