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//! Basic Calculator [leetcode: basic_calculator](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 . //! //! **Example1:** //! //! ``` //! Input: "1 + 1" //! Output: 2 //! ``` //! //! **Example2:** //! //! ``` //! Input: " 2-1 + 2 " //! Output: 3 //! ``` //! //! **Example3:** //! //! ``` //! 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. //! /// # Solutions /// /// # Approach 1: Stack /// /// * Time complexity: O(n) /// /// * Space complexity: O(n) /// /// * Runtime: 0ms /// /// Memory: 2.9MB /// /// ```rust /// impl Solution { /// pub fn calculate(s: String) -> i32 { /// let mut stack = vec![]; /// let mut operand = 0; /// let mut result = 0; /// let mut sign = 1; /// /// stack.push(sign); /// for ch in s.chars() { /// match ch { /// '0'...'9' => { /// operand = 10 * operand + (ch as u8 - '0' as u8) as i32; /// }, /// '(' => { /// stack.push(sign); /// }, /// ')' => { /// stack.pop(); /// }, /// '+' | '-' => { /// result += sign * operand; /// operand = 0; /// sign = stack.last().unwrap() * if ch == '+' { 1 } else { -1 }; /// }, /// _ => {}, /// } /// } /// result + (sign * operand) /// } /// } /// ``` /// pub fn calculate(s: String) -> i32 { let mut stack = vec![]; let mut operand = 0; let mut result = 0; let mut sign = 1; stack.push(sign); for ch in s.chars() { match ch { '0'...'9' => { operand = 10 * operand + (ch as u8 - '0' as u8) as i32; }, '(' => { stack.push(sign); }, ')' => { stack.pop(); }, '+' | '-' => { result += sign * operand; operand = 0; sign = stack.last().unwrap() * if ch == '+' { 1 } else { -1 }; }, _ => {}, } } result + (sign * operand) }