First Midterm.7 Letters (Solved)

import java.io.IOException;
import java.util.NoSuchElementException;
import java.util.Scanner;

interface Stack<E> {

    // Elementi na stekot se objekti od proizvolen tip.

    // Metodi za pristap:

    public boolean isEmpty();
    // Vrakja true ako i samo ako stekot e prazen.

    public E peek();
    // Go vrakja elementot na vrvot od stekot.

    // Metodi za transformacija:

    public void clear();
    // Go prazni stekot.

    public void push(E x);
    // Go dodava x na vrvot na stekot.

    public E pop();
    // Go otstranuva i vrakja elementot shto e na vrvot na stekot.
}

class ArrayStack<E> implements Stack<E> {
    private E[] elems;
    private int depth;

    @SuppressWarnings("unchecked")
    public ArrayStack(int maxDepth) {
        // Konstrukcija na nov, prazen stek.
        elems = (E[]) new Object[maxDepth];
        depth = 0;
    }


    public boolean isEmpty() {
        // Vrakja true ako i samo ako stekot e prazen.
        return (depth == 0);
    }


    public E peek() {
        // Go vrakja elementot na vrvot od stekot.
        if (depth == 0)
            throw new NoSuchElementException();
        return elems[depth - 1];
    }


    public void clear() {
        // Go prazni stekot.
        for (int i = 0; i < depth; i++) elems[i] = null;
        depth = 0;
    }


    public int length() {
        return depth;
    }

    public void push(E x) {
        // Go dodava x na vrvot na stekot.
        elems[depth++] = x;
    }


    public E pop() {
        // Go otstranuva i vrakja elementot shto e na vrvot na stekot.
        if (depth == 0)
            throw new NoSuchElementException();
        E topmost = elems[--depth];
        elems[depth] = null;
        return topmost;
    }
}

public class StackBukvi {
    static int proveri_t_posle_s(char symbols[]) {
        ArrayStack<Character> stack = new ArrayStack<>(symbols.length);
        for (int i = 0; i < symbols.length; i++) {
            if (symbols[i] == 'S' || symbols[i] == 'T') {
                stack.push(symbols[i]);
            }
        }

        int letterS = 0;
        int letterT = 0;
        while (!(stack.isEmpty())) {
            Character current = stack.pop();
            if (current.equals('T')) {
                letterT++;
            } else {
                /* Just looking for when it fails */
                if (letterS == 0 && letterT == 0) {
                    return 0;
                } else if (letterS == 0) {
                    letterS = letterT;
                }
                /* Occurrences of S and T do not match */
                else if (letterS != letterT) {
                    return 0;
                }
                letterT = 0;
            }
        }
        /* Didn't fail so it must be good */
        return 1;
    }

    public static void main(String[] args) throws IOException {

        Scanner f = new Scanner(System.in);
        String st = f.next();
        char niza[] = st.toCharArray();

        int rez = proveri_t_posle_s(niza);
        System.out.println(rez);
    }


}