basic-calculator

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224. Basic Calculator (Hard)

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 * 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.

Related Topics

[Stack] [Recursion] [Math] [String]

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