[Swift]LeetCode227. 基本计算器 II | Basic Calculator II

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➤微信公众号：山青咏芝（shanqingyongzhi）
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➤GitHub地址：https://github.com/strengthen/LeetCode
➤原文地址：https://www.cnblogs.com/strengthen/p/10204363.html 
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Implement a basic calculator to evaluate a simple expression string.

The expression string contains only non-negative integers, +, -, *, /operators and empty spaces . The integer division should truncate toward zero.

Example 1:

Input: "3+2*2"
Output: 7

Example 2:

Input: " 3/2 "
Output: 1

Example 3:

Input: " 3+5 / 2 "
Output: 5

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。

字符串表达式仅包含非负整数，+， - ，*，/ 四种运算符和空格  。 整数除法仅保留整数部分。

示例 1:

输入: "3+2*2"
输出: 7

示例 2:

输入: " 3/2 "
输出: 1

示例 3:

输入: " 3+5 / 2 "
输出: 5

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。

---

116ms

class Solution {
    func calculate(_ s: String) -> Int {
        var num = 0
        var sign = "+"
        var strArr = Array(s)
        var stack = [Int]()
        var res = 0

        for i in 0..<strArr.count {
            if strArr[i] >= "0" && strArr[i] <= "9" {
                num = num * 10 + Int(String(strArr[i]))!
            }

            if ((strArr[i] < "0" || strArr[i] > "9") && strArr[i] != " ") || i == strArr.count - 1 {
                if sign == "+" {
                    stack.append(num)
                } else if sign == "-" {
                    stack.append(-num)
                } else if sign == "*" {
                    stack.append(stack.removeLast() * num)
                } else if sign == "/" {
                    stack.append(stack.removeLast() / num)
                }

                sign = String(strArr[i])
                num = 0
            }
        }


        for i in stack {
            res += i
        }

        return res
    }
}

---

124ms

class Solution {
    func calculate(_ s: String) -> Int {
        var stack = [Int]()
        var str = Array(s+"+")
        
        var num = 0
        var sign: Character = "+"
        
        for char in str {
            if char >= "0" && char <= "9" {
                num = num * 10 + Int(String(char))!
            } else if operators.contains(char) {
                if sign == "+" || sign == "-"{
                    stack.append((sign == "-" ? -1 : 1) * num)
                } else if sign == "*" || sign == "/" {
                    let n = stack.removeLast()
                    stack.append(sign == "*" ? n * num : n / num)
                }
                num = 0
                sign = char
            }
        }
        return stack.reduce(0, +)
    }
    
    let operators = Set<Character>(["+", "-", "*", "/"])
}

---

140ms

class Solution {
    func calculate(_ s: String) -> Int {
        var stack = [Int]()
        var str = Array(s+"+")
        
        var num = 0
        var sign: Character = "+"
        
        for char in str {
            if operands.contains(char) {
                num = num * 10 + Int(String(char))!
            } else if operators.contains(char) {
                if sign == "+" || sign == "-"{
                    stack.append((sign == "-" ? -1 : 1) * num)
                } else if sign == "*" || sign == "/" {
                    let n = stack.removeLast()
                    stack.append(sign == "*" ? n * num : n / num)
                }
                num = 0
                sign = char
            }
        }
        return stack.reduce(0, +)
    }
    
    let operators = Set<Character>(["+", "-", "*", "/"])
    let operands = Set<Character>(["0", "1", "2", "3", "4", "5", "6", "7", "8", "9"])
}

---

228ms

class Solution {
    func calculate(_ s: String) -> Int {
        var nums: [Int] = []
        var operations: [Character] = []
        var preNum = ""
        for char in s {
            if let _ = Int(String(char)) {
                preNum += String(char)
            } else {
                if preNum != "" {
                    nums.append(Int(preNum)!)
                    preNum = ""
                }

                if !operations.isEmpty {
                    let operation = operations[operations.count - 1]
                    if nums.count > operations.count && (operation == "*" || operation == "/") {
                        let num2 = nums.popLast()!
                        let num1 = nums.popLast()!
                        if operation == "*" {
                            let num = num1 * num2
                            nums.append(num)
                        } else if operation == "/" {
                            let num = num1 / num2
                            nums.append(num)
                        }

                        operations.removeLast()
                    }
                }


                if char != " " {
                    operations.append(char)
                }
            }
        }

        if preNum != "" {
            nums.append(Int(preNum)!)
        }

        if !operations.isEmpty && operations.last == "/" || operations.last == "*" {
            let operation = operations.popLast()!
            let num2 = nums.popLast()!
            let num1 = nums.popLast()!
            if operation == "*" {
                nums.append(num1 * num2)
            } else if operation == "/" {
                nums.append(num1 / num2)
            }
        }
    
        nums.reverse()
        for operation in operations {
            let num1 = nums.popLast()!
            let num2 = nums.popLast()!
            if operation == "+" {
                nums.append(num1 + num2)
            } else if operation == "-" {
                nums.append(num1 - num2)
            } else if operation == "*" {
                nums.append(num1 * num2)
            } else if operation == "/" {
                nums.append(num1 / num2)
            }
        }

        return nums.isEmpty ? 0 : nums[0]
    }
}

---

548ms

class Solution {
    func calculate(_ s: String) -> Int {
        var numStack = [Int]()
        var opeStack = [String]()
        let sArr = Array(s)
        let nums = "0123456789"
        let opes = "+-*/"
        
        var i = 0
        while i < sArr.count {
            let c = sArr[i]
            if nums.contains(c) {
                var tmp = 0
                while i < sArr.count && nums.contains(sArr[i]) {
                    tmp = tmp * 10 + Int(String(sArr[i]))!
                    i += 1
                }
                if let ope = opeStack.last, ope == "*" || ope ==  "/" {
                    let last = numStack.removeLast()
                    opeStack.removeLast()
                    if ope == "*" {
                        tmp *= last
                    }else if ope == "/" {
                        tmp = last / tmp
                    }
                    
                }
                numStack.append(tmp)
                i -= 1
            }else if opes.contains(c) {
                opeStack.append(String(c))
            }
            
            i += 1
        }
        
        var res = numStack.first ?? 0
        
        for i in 0..<opeStack.count {
            let ope = opeStack[i]
            if ope == "+" {
                res += numStack[i+1]
            }else if ope == "-" {
                res -= numStack[i+1]
            }
        }
        return res
    }
}