224. Basic Calculator (Hard)
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: 23Note:
- You may assume that the given expression is always valid.
- Do not use the
evalbuilt-in library function.