Basic Calculator
Given a valid arithmetic expression string s, evaluate it and return its integer result.
The expression may contain non-negative integers, + and - operators, parentheses, and spaces. Spaces should be ignored.
You may not use a built-in expression evaluator.
Input & Output
Input
s — Valid arithmetic expression containing numbers, plus, minus, parentheses, and spaces
Output
The evaluated integer result
Example
Input
s = 1 + 1
Output
2
Explanation
1 + 1 = 2.
Example
Input
s = 2-1 + 2
Output
3
Explanation
2 - 1 + 2 = 3.
Example
Input
s = 1 - (2 + 3)
Output
-4
Explanation
The - applies to the whole group: 1 - (2 + 3) = 1 - 5 = -4. Just dropping the parentheses would give 1 - 2 + 3 = 2, so a minus in front of a ( is exactly why the parentheses matter.
Example
Input
s = (1+(4+5+2)-3)+(6+8)
Output
23
Explanation
The first parenthesized group evaluates to 9, and the second group evaluates to 14.
Constraints
1 <= s.lengthsis a valid expression containing digits,+,-,(,), and spaces- Every number is a non-negative integer