Basic Calculator
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
2The expression
1 + 1 evaluates to 2.Example 2
Input
s = " 2-1 + 2 "Output
3The expression
2 - 1 + 2 evaluates to 3.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.