[Swift]LeetCode1106. 解析布爾表達式 | Parsing A Boolean Expression

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➤微信公衆號：山青詠芝（shanqingyongzhi）
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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.

---

給你一個以字符串形式表述的 布爾表達式（boolean） expression，返回該式的運算結果。

有效的表達式需遵循如下約定：

• "t"，運算結果爲 True
• "f"，運算結果爲 False
• "!(expr)"，運算過程爲對內部表達式 expr 進行邏輯 非的運算（NOT）
• "&(expr1,expr2,...)"，運算過程爲對 2 個或以上內部表達式 expr1, expr2, ... 進行邏輯 與的運算（AND）
• "|(expr1,expr2,...)"，運算過程爲對 2 個或以上內部表達式 expr1, expr2, ... 進行邏輯 或的運算（OR）

示例 1：

輸入：expression = "!(f)"
輸出：true

示例 2：

輸入：expression = "|(f,t)"
輸出：true

示例 3：

輸入：expression = "&(t,f)"
輸出：false

示例 4：

輸入：expression = "|(&(t,f,t),!(t))"
輸出：false 

提示：

• 1 <= expression.length <= 20000
• expression[i] 由 {'(', ')', '&', '|', '!', 't', 'f', ','} 中的字符組成。
• expression 是以上述形式給出的有效表達式，表示一個布爾值。

---

Runtime: 32 ms

Memory Usage: 20.8 MB

 1 class Solution {
 2     func parseBoolExpr(_ expression: String) -> Bool {
 3         var op:[Character] = [Character]()
 4         var num:[Int] = [Int]()
 5         for ch in expression
 6         {
 7             if ch == "t" {num.append(1)}
 8             else if ch == "f" {num.append(0)}
 9             else if (ch == "|") || (ch == "&") || (ch == "!") {op.append(ch)}
10             else if ch == "(" {num.append(-1)}
11             else if ch == "," {continue}
12             else if ch == ")"
13             {
14                 var ans:Int = num.popLast()!
15                 let p:Character = op.popLast()!
16                 while(num.last! != -1)
17                 {
18                     let a:Int = num.popLast()!
19                     if p == "&" {ans = ans & a}
20                     else if p == "|" {ans = ans | a}
21                 }
22                 num.popLast()
23                 if p == "!" {ans =  1 - ans}
24                 num.append(ans)
25             }
26         }
27         if num.last! == 1
28         {
29             return true
30         }
31         return false
32     }
33 }

 

---

72ms

 

 1 class Solution {
 2     var expressions : [Character] = ["&","|","!"]
 3     var bools : [Character] = ["t","f"]
 4     func parseBoolExpr(_ expression: String) -> Bool {
 5         var stack : String = ""
 6         let expression = Array(expression)
 7         
 8         _ = true
 9         var currentBools = [Character]()
10         for i in 0..<expression.count {
11             
12             if expression[i] == ")" {
13                 while let head = stack.popLast(), head != "(" {
14                     if head == "t" || head == "f" {
15                         currentBools.append(head)
16                     }
17                 }
18                 if let op = stack.popLast() {
19                     if op == "&" {
20                         stack.append(evaluateAND(currentBools))
21                         currentBools.removeAll()
22                     } else if op == "|" {
23                         stack.append(evaluateOR(currentBools))
24                         currentBools.removeAll()
25                     } else if op == "!" {
26                         stack.append(evaluateNot(currentBools.first!))
27                         currentBools.removeAll()
28                     }
29                     continue
30                 }
31             }
32             if bools.contains(expression[i]) {
33                 currentBools.append(expression[i])
34                 continue
35             }
36             
37             stack.append(expression[i])
38         }
39         if stack.popLast() == "t" {return true}
40         return false
41     }
42     
43     func evaluateOR (_ input: [Character]) -> Character {
44         if input.contains("t") {return "t"}
45         return "f"
46     }
47     
48     func evaluateAND (_ input: [Character]) -> Character {
49         if input.contains("f") {return "f"}
50         return "t"
51     }
52     
53     func evaluateNot(_ input: Character) -> Character {
54         if input == ("f") {return "t"}
55         return "f"
56     }
57 }