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Basic Calculator
Given a string s representing a valid expression, implement a basic calculator to evaluate it, and return the result of the evaluation.
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().
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 * 10^5
- 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.
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