[Swift]LeetCode1106. 解析布尔表达式 | Parsing A Boolean Expression

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Return the result of evaluating a given boolean expression, represented as a string.

An expression can either be:

• "t", evaluating to True;
• "f", evaluating to False;
• "!(expr)", evaluating to the logical NOT of the inner expression expr;
• "&(expr1,expr2,...)", evaluating to the logical AND of 2 or more inner expressions expr1, expr2, ...;
• "|(expr1,expr2,...)", evaluating to the logical OR of 2 or more inner expressions expr1, expr2, ... 

Example 1:

Input: expression = "!(f)"
Output: true

Example 2:

Input: expression = "|(f,t)"
Output: true

Example 3:

Input: expression = "&(t,f)"
Output: false

Example 4:

Input: expression = "|(&(t,f,t),!(t))"
Output: false 

Constraints:

• 1 <= expression.length <= 20000
• expression[i] consists of characters in {'(', ')', '&', '|', '!', 't', 'f', ','}.
• expression is a valid expression representing a boolean, as given in the description.

---

给你一个以字符串形式表述的 布尔表达式（boolean） expression，返回该式的运算结果。

有效的表达式需遵循以下约定：

• "t"，运算结果为 True
• "f"，运算结果为 False
• "!(expr)"，运算过程为对内部表达式 expr 进行逻辑 非的运算（NOT）
• "&(expr1,expr2,...)"，运算过程为对 2 个或以上内部表达式 expr1, expr2, ... 进行逻辑 与的运算（AND）
• "|(expr1,expr2,...)"，运算过程为对 2 个或以上内部表达式 expr1, expr2, ... 进行逻辑 或的运算（OR）

示例 1：

输入：expression = "!(f)"
输出：true

示例 2：

输入：expression = "|(f,t)"
输出：true

示例 3：

输入：expression = "&(t,f)"
输出：false

示例 4：

输入：expression = "|(&(t,f,t),!(t))"
输出：false 

提示：

• 1 <= expression.length <= 20000
• expression[i] 由 {'(', ')', '&', '|', '!', 't', 'f', ','} 中的字符组成。
• expression 是以上述形式给出的有效表达式，表示一个布尔值。

---

Runtime: 32 ms

Memory Usage: 20.8 MB

class Solution {
    func parseBoolExpr(_ expression: String) -> Bool {
        var op:[Character] = [Character]()
        var num:[Int] = [Int]()
        for ch in expression
        {
            if ch == "t" {num.append(1)}
            else if ch == "f" {num.append(0)}
            else if (ch == "|") || (ch == "&") || (ch == "!") {op.append(ch)}
            else if ch == "(" {num.append(-1)}
            else if ch == "," {continue}
            else if ch == ")"
            {
                var ans:Int = num.popLast()!
                let p:Character = op.popLast()!
                while(num.last! != -1)
                {
                    let a:Int = num.popLast()!
                    if p == "&" {ans = ans & a}
                    else if p == "|" {ans = ans | a}
                }
                num.popLast()
                if p == "!" {ans =  1 - ans}
                num.append(ans)
            }
        }
        if num.last! == 1
        {
            return true
        }
        return false
    }
}

---

72ms

class Solution {
    var expressions : [Character] = ["&","|","!"]
    var bools : [Character] = ["t","f"]
    func parseBoolExpr(_ expression: String) -> Bool {
        var stack : String = ""
        let expression = Array(expression)
        
        _ = true
        var currentBools = [Character]()
        for i in 0..<expression.count {
            
            if expression[i] == ")" {
                while let head = stack.popLast(), head != "(" {
                    if head == "t" || head == "f" {
                        currentBools.append(head)
                    }
                }
                if let op = stack.popLast() {
                    if op == "&" {
                        stack.append(evaluateAND(currentBools))
                        currentBools.removeAll()
                    } else if op == "|" {
                        stack.append(evaluateOR(currentBools))
                        currentBools.removeAll()
                    } else if op == "!" {
                        stack.append(evaluateNot(currentBools.first!))
                        currentBools.removeAll()
                    }
                    continue
                }
            }
            if bools.contains(expression[i]) {
                currentBools.append(expression[i])
                continue
            }
            
            stack.append(expression[i])
        }
        if stack.popLast() == "t" {return true}
        return false
    }
    
    func evaluateOR (_ input: [Character]) -> Character {
        if input.contains("t") {return "t"}
        return "f"
    }
    
    func evaluateAND (_ input: [Character]) -> Character {
        if input.contains("f") {return "f"}
        return "t"
    }
    
    func evaluateNot(_ input: Character) -> Character {
        if input == ("f") {return "t"}
        return "f"
    }
}