Remove brackets from an algebraic string containing + and – operators

// Java program to simplify algebraic string 
import java.util.*; 
class GfG {  
  
// Function to simplify the string  
static String simplify(String str)  
{  
    int len = str.length();  
  
    // resultant string of max length equal  
    // to length of input string  
    char res[] = new char[len];  
    int index = 0, i = 0;  
  
    // create empty stack  
    Stack<Integer> s = new Stack<Integer> ();  
    s.push(0);  
  
    while (i < len) {  
        if (str.charAt(i) == '+') {  
  
            // If top is 1, flip the operator  
            if (s.peek() == 1)  
                res[index++] = '-';  
  
            // If top is 0, append the same operator  
            if (s.peek() == 0)  
                res[index++] = '+';  
  
        } else if (str.charAt(i) == '-') {  
            if (s.peek() == 1)  
                res[index++] = '+';  
            else if (s.peek() == 0)  
                res[index++] = '-';  
        } else if (str.charAt(i) == '(' && i > 0) {  
            if (str.charAt(i - 1) == '-') {  
  
                // x is opposite to the top of stack  
                int x = (s.peek() == 1) ? 0 : 1;  
                s.push(x);  
            }  
  
            // push value equal to top of the stack  
            else if (str.charAt(i - 1) == '+')  
                s.push(s.peek());  
        }  
  
        // If closing parentheses pop the stack once  
        else if (str.charAt(i) == ')')  
            s.pop();  
  
        // copy the character to the result  
        else
            res[index++] = str.charAt(i);  
        i++;  
    }  
    return new String(res);  
}  
  
// Driver program  
public static void main(String[] args)  
{  
    String s1 = "a-(b+c)";  
    String s2 = "a-(b-c-(d+e))-f";  
    System.out.println(simplify(s1));  
    System.out.println(simplify(s2)); 
} 
}