**Basic Calculator** ===================== **Problem Statement** -------------------- Given a string `s` representing a mathematical expression with parentheses, create a function to evaluate the expression and return the result as a number. The valid operators in the expression are `+`, `-`, `*`, and `/`. The expression may contain multiple spaces between operators and operands. The expression may also contain nested parentheses. Your function should support non-negative integers and decimal numbers. **Rules and Constraints** ------------------------- * The input string `s` will only contain digits, `+`, `-`, `*`, `/`, and parentheses. There will be at most one `+`, `-`, `*`, or `/` operator between each operand. * The input string `s` is guaranteed to contain at least one operand and at most one `+` or `-` operator. * There will not be any division by zero in the input string `s`. * The input string `s` will not contain any invalid expressions that would cause a stack overflow. * Your function should return a non-negative number as the result. **Output** ---------- Your function should return the result of the mathematical expression as a number. The result may be a decimal number if the input expression contains decimal points. ### Example **Input:** {"s":"1 + 1"} **Output:** 2