[Swift]LeetCode844. 比較含退格的字符串 | Backspace String Compare

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➤微信公衆號：山青詠芝（shanqingyongzhi）
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Given two strings S and T, return if they are equal when both are typed into empty text editors. # means a backspace character.

Example 1:

Input: S = "ab#c", T = "ad#c" Output: true Explanation: Both S and T become "ac". 

Example 2:

Input: S = "ab##", T = "c#d#" Output: true Explanation: Both S and T become "". 

Example 3:

Input: S = "a##c", T = "#a#c" Output: true Explanation: Both S and T become "c". 

Example 4:

Input: S = "a#c", T = "b" Output: false Explanation: S becomes "c" while T becomes "b". 

Note:

1. 1 <= S.length <= 200
2. 1 <= T.length <= 200
3. S and T only contain lowercase letters and '#' characters.

Follow up:

• Can you solve it in O(N) time and O(1) space?

---

給定 S 和 T 兩個字符串，當它們分別被輸入到空白的文本編輯器後，判斷兩者是否相等，並返回結果。 # 表明退格字符。

示例 1：

輸入：S = "ab#c", T = "ad#c"
輸出：true
解釋：S 和 T 都會變成 「ac」。

示例 2：

輸入：S = "ab##", T = "c#d#"
輸出：true
解釋：S 和 T 都會變成 「」。

示例 3：

輸入：S = "a##c", T = "#a#c"
輸出：true
解釋：S 和 T 都會變成 「c」。

示例 4：

輸入：S = "a#c", T = "b"
輸出：false
解釋：S 會變成 「c」，但 T 仍然是 「b」。

提示：

1. 1 <= S.length <= 200
2. 1 <= T.length <= 200
3. S 和 T 只含有小寫字母以及字符 '#'。

---

Runtime: 8 ms

Memory Usage: 19.5 MB

 1 class Solution {
 2     func backspaceCompare(_ S: String, _ T: String) -> Bool 
 3     {
 4         var arrS = [Character]()
 5         var arrT = [Character]()
 6         for char in S
 7         {
 8             if char == "#"
 9             {
10                 if arrS.count > 0
11                 {
12                     arrS.removeLast()
13                 }
14             }
15             else
16             {
17                 arrS.append(char)
18             }
19         }
20         
21         for char in T
22         {
23             if char == "#"
24             {
25                 if arrT.count > 0
26                 {
27                     arrT.removeLast()
28                 }
29             }
30             else
31             {
32                 arrT.append(char)
33             }
34         }
35         return arrS == arrT
36     }    
37 }

---

8ms

 1 class Solution {
 2     // S2: two pointers space could be 1
 3     // S1: M+N
 4     func backspaceCompare(_ S: String, _ T: String) -> Bool {
 5         return process(S) == process(T)    
 6     }
 7     
 8     private func process(_ S: String) -> String {
 9         var stack = [Character]()
10         for c in Array(S) {
11             if c == "#" {
12                 if stack.count > 0 {
13                     stack.removeLast()
14                 }
15             } else {
16                 stack.append(c)
17             }
18         }
19         return String(stack)
20     }
21 }

---

12ms

 1 class Solution {
 2     func backspaceCompare(_ S: String, _ T: String) -> Bool {
 3         var sStack: [Character] = []
 4         var tStack: [Character] = []
 5 
 6         var sArray = Array(S)
 7         var tArray = Array(T)
 8         
 9         for char in sArray {
10             if(char != "#") {
11                 sStack.append(char)
12             } else {
13                 if(!sStack.isEmpty) {
14                     sStack.removeLast()   
15                 }
16             }
17         }
18         
19         for char in tArray {
20             if(char != "#") {
21                 tStack.append(char)
22             } else {
23                 if(!tStack.isEmpty) {
24                     tStack.removeLast()   
25                 }
26             }
27         }
28         
29         print(String(sStack))
30         print(String(tStack))
31         
32         if(String(sStack) == String(tStack)) {
33             return true
34         } else {
35             return false
36         }
37     }
38 }

---

16ms

 1 class Solution {
 2     func backspaceCompare(_ S: String, _ T: String) -> Bool {
 3         var charsS = Array(S), charsT = Array(T)
 4         
 5         var i = charsS.count - 1, j = charsT.count - 1
 6         var countS = 0, countT = 0
 7         while i >= 0 || j >= 0 {
 8             while i >= 0 && (countS > 0 || charsS[i] == "#") { 
 9                 if charsS[i] == "#" { 
10                     countS += 1
11                 } else {
12                     countS -= 1
13                 }
14                 
15                 i -= 1
16             }
17             
18             while j >= 0 && (countT > 0 || charsT[j] == "#") { 
19                 if charsT[j] == "#" { 
20                     countT += 1
21                 } else {
22                     countT -= 1
23                 }
24                 
25                 j -= 1
26             }
27             
28             if i >= 0 && j >= 0 && charsS[i] == charsT[j] {
29                 i -= 1
30                 j -= 1 
31             } else {
32                 break
33             }
34         }
35         return i < 0 && j < 0
36     }
37 }

---

24ms

 1 class Solution {
 2     func backspaceCompare(_ S: String, _ T: String) -> Bool {
 3         return backspace(S) == backspace(T)
 4     }
 5     
 6     func backspace(_ string: String) -> String {
 7         var s = [Character]()
 8 
 9         string.forEach { c in
10             if c == "#" {
11                 if !s.isEmpty {
12                     s.removeLast()
13                 }
14             } else {
15                 s.append(c)
16             }
17         }
18         return String(s)
19     }
20 }

---

24ms

 1 class Solution {
 2     func backspaceCompare(_ S: String, _ T: String) -> Bool {
 3         let sRe = reStack(str: S)
 4         let tRe = reStack(str: T)
 5         return sRe == tRe;
 6     }
 7     
 8     public func reStack(str: String) -> String {
 9         var result = [Character]()
10         for i in str {
11             if (!result.isEmpty) {
12                 if i != "#" {
13                     result.append(i)
14                 } else {
15                     result.removeLast()
16                 }
17             } else {
18                 if i != "#" {
19                     result.append(i)
20                 }
21             }
22         }
23         return String.init(result);
24     }
25 }