[Swift]LeetCode777. 在LR字符串中交換相鄰字符 | Swap Adjacent in LR String

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In a string composed of 'L', 'R', and 'X'characters, like "RXXLRXRXL", a move consists of either replacing one occurrence of "XL" with "LX", or replacing one occurrence of "RX" with "XR". Given the starting string start and the ending string end, return True if and only if there exists a sequence of moves to transform one string to the other.

Example:

Input: start = "RXXLRXRXL", end = "XRLXXRRLX"
Output: True
Explanation:
We can transform start to end following these steps:
RXXLRXRXL ->
XRXLRXRXL ->
XRLXRXRXL ->
XRLXXRRXL ->
XRLXXRRLX

Note:

1. 1 <= len(start) = len(end) <= 10000.
2. Both start and end will only consist of characters in {'L', 'R', 'X'}.

---

在一個由 'L' , 'R' 和 'X' 三個字符組成的字符串（例如"RXXLRXRXL"）中進行移動操做。一次移動操做指用一個"LX"替換一個"XL"，或者用一個"XR"替換一個"RX"。現給定起始字符串start和結束字符串end，請編寫代碼，當且僅當存在一系列移動操做使得start能夠轉換成end時， 返回True。

示例 :

輸入: start = "RXXLRXRXL", end = "XRLXXRRLX"
輸出: True
解釋:
咱們能夠經過如下幾步將start轉換成end:
RXXLRXRXL ->
XRXLRXRXL ->
XRLXRXRXL ->
XRLXXRRXL ->
XRLXXRRLX

注意:

1. 1 <= len(start) = len(end) <= 10000。
2. start和end中的字符串僅限於'L', 'R'和'X'。

---

Runtime: 24 ms

Memory Usage: 19.5 MB

 1 class Solution {
 2     func canTransform(_ start: String, _ end: String) -> Bool {
 3         var start = Array(start)
 4         var end = Array(end)
 5         var n:Int = start.count
 6         var cntL:Int = 0
 7         var cntR:Int = 0
 8         for i in 0..<n
 9         {
10             if start[i] == "R" {cntR += 1}
11             if end[i] == "L" {cntL += 1}
12             if start[i] == "L" {cntL -= 1}
13             if end[i] == "R" {cntR -= 1}
14             if cntL < 0 || cntR < 0 || cntL * cntR != 0
15             {
16                 return false
17             }
18         }
19         return cntL == 0 && cntR == 0
20     }
21 }

---

68ms

 1 class Solution {
 2     func canTransform(_ start: String, _ end: String) -> Bool {
 3         let cs = Array(start)
 4         let ce = Array(end)
 5         let ts = String(cs.filter{ $0 != "X" } )
 6         let te = String(ce.filter{ $0 != "X" } )
 7                                            
 8         guard ts == te else { return false }
 9         
10         var sr = [Int]()
11         var sl = [Int]()
12         
13         for (i, char) in cs.enumerated() {
14             if char == "R" {
15                 sr.append(i)
16             } else if char == "L" {
17                 sl.append(i)
18             }
19         }
20         
21         var rCount = 0
22         var lCount = 0
23         
24         for (i, char) in ce.enumerated() {
25             if char == "R" {
26                 if sr[rCount] > i {
27                     return false
28                 } else {
29                     rCount += 1
30                 }
31             } else if char == "L" {
32                 if sl[lCount] < i {
33                     return false
34                 } else {
35                     lCount += 1
36                 }
37             }
38         } 
39         
40         return true
41     }
42 }

---

96ms

 1 class Solution {    
 2     func compare(_ start: String, _ end: String) -> Bool {
 3         var rs1 = 0
 4         var ls1 = 0
 5         var xs1 = 0 
 6         var rs2 = 0
 7         var ls2 = 0
 8         var xs2 = 0
 9         for i in start.indices {
10             switch start[i] {
11                 case "R":
12                     rs1 += 1
13                 case "L":
14                     ls1 += 1
15                 case "X":
16                     xs1 += 1
17                 default:
18                     break
19             }
20             switch end[i] {
21                 case "R":
22                     rs2 += 1
23                 case "L":
24                     ls2 += 1
25                 case "X":
26                     xs2 += 1
27                 default:
28                     break
29             }
30         }
31         return rs1 == rs2 && ls1 == ls2 && xs1 == xs2
32     }
33     
34     func canTransform(_ start: String, _ end: String) -> Bool {
35         var rs = [String.Index]()
36         var ls = [String.Index]()
37         for (i, ch) in zip(start.indices, start) {
38             if ch == "R" {
39                 rs.append(i)
40             } else if ch == "L" {
41                 ls.append(i)
42             }
43         }
44         rs.reverse()
45         ls.reverse()
46         
47         if !compare(start, end) {
48             return false
49         }
50         
51         for (i, ch) in zip(end.indices, end) {
52             if ch == "R" {
53                 if let nextRIdx = rs.last, nextRIdx <= i {
54                     if let nextLIdx = ls.last {
55                         if nextLIdx < nextRIdx {
56                             // impossible to move R through L
57                             return false
58                         } else {
59                             rs.removeLast()
60                         }
61                     } else {
62                         rs.removeLast()
63                     }
64                 } else {
65                     return false
66                 }
67             } else if ch == "L" {
68                 if let nextLIdx = ls.last, nextLIdx >= i {
69                     if let nextRIdx = rs.last {
70                         if nextRIdx < nextLIdx {
71                             // impossible to move L through R
72                             return false
73                         } else {
74                             ls.removeLast()
75                         }
76                     } else {
77                         ls.removeLast()
78                     }
79                 } else {
80                     return false
81                 }
82             }
83         }
84         return true
85     }
86 }

---

104ms

 1 class Solution {
 2     func canTransform(_ start: String, _ end: String) -> Bool {
 3         guard start.count >= 1 && start.count <= 10000 && end.count >= 1 && end.count <= 10000 else {
 4             return false
 5         }
 6         let startChars = Array(start), endChars = Array(end)
 7         var startInfos = [(Character, Int)](), endInfos = [(Character, Int)]()
 8         for (index, char) in startChars.enumerated() {
 9             if char == "L" || char == "R" {
10                 startInfos.append((char, index))
11             } else if char != "X" {
12                 return false
13             }
14         }
15         for (index, char) in endChars.enumerated() {
16             if char == "L" || char == "R" {
17                 endInfos.append((char, index))
18             } else if char != "X" {
19                 return false
20             }
21         }
22         let startInfosChars = startInfos.map {
23             $0.0
24         }
25         let endInfosChars = endInfos.map {
26             $0.0
27         }
28         guard startInfosChars == endInfosChars else {
29             return false
30         }
31         for (index, startInfo) in startInfos.enumerated() {
32             let endInfo = endInfos[index]
33             if startInfo.0 == "L" {
34                 guard startInfo.1 >= endInfo.1 else {
35                     return false
36                 }
37             } else {
38                 guard startInfo.1 <= endInfo.1 else {
39                     return false
40                 }
41             }
42         }
43         return true
44     }
45 }