Basic Calculator

Implement a basic calculator that evaluates a given mathematical expression represented as a string.

Constraints:

• The input string s will have a length between 1 and 3 * 10^5 characters.
• The string s will only contain digits, '+', '-', '(', ')', and spaces.
• The expression represented by s is guaranteed to be valid.
• Unary plus (+) will not be used (e.g., +1 or +(2 + 3) are invalid).
• Unary minus (-) is permitted (e.g., -1 or -(2 + 3) are valid).
• There will be no consecutive operators.
• All intermediate and final results will fit within a signed 32-bit integer.

Note: You are not allowed to use any built-in functions that evaluate strings as mathematical expressions (e.g., eval()).

Examples:

• Input: s = "1 + 1" Output: 2

• Input: s = " 2-1 + 2 " Output: 3

• Input: s = "(1+(4+5+2)-3)+(6+8)" Output: 23

Similar LeetCode problem: Basic Calculator