224. Basic Calculator

Hard

50 Points

Math

String

Stack

Recursion

Given a string s representing a valid expression, implement a basic calculator to evaluate it, and return the result of the evaluation. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions, such as eval().

Examples

Example 1

Input: s = "1 + 1" Output: 2

Example 2

Input: s = " 2-1 + 2 " Output: 3

Example 3

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

Constraints

1 <= s.length <= 3 * 105
s consists of digits, '+', '-', '(', ')', and ' '.
s represents a valid expression.
'+' is not used as a unary operation (i.e., "+1" and "+(2 + 3)" is invalid).
'-' could be used as a unary operation (i.e., "-1" and "-(2 + 3)" is valid).
There will be no two consecutive operators in the input.
Every number and running calculation will fit in a signed 32-bit integer.