224. Basic Calculator

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https://leetcode.com/problems/basic-calculator/

Implement a basic calculator to evaluate a simple expression string.

The expression string may contain open ( and closing parentheses ), the plus + or minus sign -, non-negative integers and empty spaces .

Example 1:

Input: "1 + 1"
Output: 2

Example 2:

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

Example 3:

Input: "(1+(4+5+2)-3)+(6+8)"
Output: 23
Note:
  • You may assume that the given expression is always valid.
  • Do not use the eval built-in library function.
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