[Swift]LeetCode224. 基本计算器 | Basic Calculator

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➤微信公众号：山青咏芝（shanqingyongzhi）
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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.

---

实现一个基本的计算器来计算一个简单的字符串表达式的值。

字符串表达式可以包含左括号 ( ，右括号 )，加号 + ，减号 -，非负整数和空格  。

示例 1:

输入: "1 + 1"
输出: 2

示例 2:

输入: " 2-1 + 2 "
输出: 3

示例 3:

输入: "(1+(4+5+2)-3)+(6+8)"
输出: 23

说明：

• 你可以假设所给定的表达式都是有效的。
• 请不要使用内置的库函数 eval。

---

96ms

class Solution {
    func calculate(_ s: String) -> Int {
        var num = 0
        var res = 0
        var sign = 1
        var stack = [Int]()
        var s = Array(s)
        for i in 0 ..< s.count {
            var c = s[i]
            
            if c == "+" {
                res += sign*num
                num = 0
                sign = 1
            } else if c == "-" {
                res += sign*num
                num = 0
                sign = -1
            } else if c == "(" {
                stack.append(res)
                stack.append(sign)
                res = 0
                sign = 1
            } else if c == ")" {
                res += sign*num
                num = 0
                res *= stack.removeLast()
                res += stack.removeLast()
            } else {
                if let n = Int(String(c)) {
                    num = 10*num+n
                }
            }
        }
        
        if num != 0 {
            res += sign*num
        }
        return res
    }
}

---

132ms

class Solution {
    func calculate(_ s: String) -> Int {
        var res = 0
        var num = 0
        var sign = 1
        var stack = [Int]()
        let sArray = Array(s)
        
        for i in 0..<sArray.count {
            if let value = Int(String(sArray[i])) {
                num = num * 10 + value
            }else if sArray[i] == "+" || sArray[i] == "-" {
                res += sign * num
                sign = sArray[i] == "+" ? 1 : -1
                num = 0
            }else if sArray[i] == "(" {
                stack.append(res)
                stack.append(sign)
                sign = 1
                res = 0
            }else if sArray[i] == ")" {
                res += num * sign
                let tmp = res * stack.removeLast()
                res = stack.removeLast() + tmp
                sign = 1
                num = 0
            }
        }
        
        return num == 0 ? res : res + sign * num
    }
}

---

144ms

class Solution {
    func calculate(_ s: String) -> Int {
        var result = 0
        var num = 0
        var sign = 1
        var equationStack = [Int]()

        for char in s {
            if let digit = Int(String(char)) {
                num = 10 * num + digit
            } else if char == "+" {
                result += sign * num
                num = 0
                sign = 1
            } else if char == "-" {
                result += sign * num
                num = 0
                sign = -1
            } else if char == "(" {
                equationStack.append(result)
                equationStack.append(sign)
                sign = 1
                result = 0
            } else if char == ")" {
                result += sign * num
                num = 0
                result *= equationStack.removeLast()
                result += equationStack.removeLast()
            }
        }
        if num != 0 { result += sign * num }
        return result
    }
}

---

192ms

class Solution {
    func calculate(_ s: String) -> Int {
        var res = 0, num = 0, sign = 1, n = s.count
        var st = [Int]()
        for c in s {
            if c == " " { continue }
            else if c == "+" || c == "-" {
                res += sign*num
                num = 0
                sign = (c == "+") ? 1: -1
            }
            else if c == "(" {
                st.append(res)
                st.append(sign)
                res = 0
                sign = 1
            }
            else if c == ")" {
                res += sign*num
                num = 0
                res *= st.removeLast()
                res += st.removeLast()
                
            }
            else {
                num = num*10 + Int(String(c))!
            }
        }
                        res += sign*num

        return res
    }
}

---

196ms

class Solution {
    func calculate(_ s: String) -> Int {
        let trimmedS = s.trimmingCharacters(in: .whitespaces)
        let charArray = [Character](trimmedS)
        var stack = [Int]()
        var num = 0
        var result = 0
        var sign = 1
        
        for i in 0..<charArray.count{
         
            if let digit = Int(String(charArray[i])){     
                num = num*10 + digit
                if (i < charArray.count - 1 && Int(String(charArray[i + 1])) == nil) || i == charArray.count - 1{
                     result += num*sign
                }
            }else{
                num = 0
                if charArray[i] == "+"{
                    sign = 1
                }else if charArray[i] == "-"{
                    sign = -1
                }else if charArray[i] == "("{
                    stack.append(result)
                    stack.append(sign)
                    result = 0
                    sign = 1
                }else if charArray[i] == ")"{
                    let signBeforeParenthese = stack.removeLast()
                    let resultBeforeParenthese = stack.removeLast()
                    result =  resultBeforeParenthese + signBeforeParenthese*result
                }else{
                    continue
                }
            }

        }
        return result

    }
}

---

344ms

class Solution {
    func calculate(_ s: String) -> Int {
        var s = Array(s.characters)
        var tk_i = 0
        func nextToken() -> String? {
            if tk_i >= s.count { return nil }
            if s[tk_i] == " " {
                tk_i += 1
                return nextToken() 
            }
            if s[tk_i] >= "0" && s[tk_i] <= "9" {
                var j = tk_i + 1
                while j < s.count && s[j] >= "0" && s[j] <= "9" { j += 1 }
                let ret = String(s[tk_i..<j])
                tk_i = j
                return ret
            }
            tk_i += 1
            return String(s[tk_i - 1])
        }
        
        var stack = [String]()
        func eval(_ from: Int, _ to: Int) -> Int {
            var ret = Int(stack[from])!
            var i = from + 1
            while i <= to {
                let opr = stack[i]
                let opnd = Int(stack[i + 1])!
                if opr == "+" {
                    ret = ret + opnd
                } else {
                    ret = ret - opnd
                }
                i += 2
            }
            return ret
        }
            
        while let tk = nextToken() {
            if tk == ")" {
                var j = stack.count - 1
                while stack[j] != "(" { j -= 1 }
                let res = eval(j + 1, stack.count - 1)
                while stack.count > j { stack.removeLast() }
                stack.append(String(res))
            } else {
                stack.append(tk)
            }
        }
        
        return eval(0, stack.count - 1)
    }
}