class Solution {

public int calculate(String s) {

Stack<Integer> stack = new Stack<>();

int result = 0;

int number = 0;

int sign = 1;

for (int i = 0; i < s.length(); i++) {

char c = s.charAt(i);

if (Character.isDigit(c)) {

number = number * 10 + Character.getNumericValue(c);

} else if (c == '+' || c == '-') {

result += sign * number;

sign = c == '+' ? 1 : -1;

number = 0;

} else if (c == '(') {

stack.push(result);

stack.push(sign);

sign = 1;

result = 0;

} else if (c == ')') {

result += sign * number;

result *= stack.pop();

result += stack.pop();

number = 0;

}

}

return result + (sign * number);

}

}