1.3

import java.util.Stack;
public class Practice
{
    public static void main(String[] args)
    {
        String a = "[()]{}{[()]}";
        String b = "[(])";
        System.out.println(isLegal(a));
        System.out.println(isLegal(b));
    }
    public static boolean isLegal(String string)
    {
        Stack<Character> stack = new Stack<Character>();
        for (int i = 0; i < string.length(); ++i)
        {
            char c = string.charAt(i);
            if (c == '[' || c == '(' || c == '{')
            {
                stack.push(c);
            }
            else if (c == ')')
            {
                char temp = stack.pop();
                if (temp != '(')
                    return false;
            }
            else if (c == ']')
            {
                char temp = stack.pop();
                if (temp != '[')
                    return false;
            }
            else if (c == '}')
            {
                char temp = stack.pop();
                if (temp != '{')
                    return false;
            }
        }
        return true;
    }
}

import java.util.Stack;
public class Practice
{
    public static void main(String[] args)
    {
        String s = "1 + 2 ) * 3 - 4 ) * 5 - 6 ) ) )";
        Stack<String> stack = new Stack<>();
        Stack<String> num = new Stack<>();
        String[] strings = s.split(" ");
        for (int i = 0; i < strings.length; ++i)
        {
            if (strings[i].equals("+") || strings[i].equals("-") || strings[i].equals("*") || strings[i].equals("/"))
            {
                stack.push(strings[i]);
            }
            else if (strings[i].equals(")"))
            {
                String string = "(";
                String a = num.pop();
                String b = num.pop();
                string += b + stack.pop() + a + ")";
                num.push(string);
            }
            else
                num.push(strings[i]);
        }
        System.out.println(num.pop());
    }
}