[Swift]LeetCode777. 在LR字符串中交换相邻字符 | 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'}.

---

在一个由 'L' , 'R' 和 'X' 三个字符组成的字符串（例如"RXXLRXRXL"）中进行移动操作。一次移动操作指用一个"LX"替换一个"XL"，或者用一个"XR"替换一个"RX"。现给定起始字符串start和结束字符串end，请编写代码，当且仅当存在一系列移动操作使得start可以转换成end时， 返回True。

示例 :

输入: start = "RXXLRXRXL", end = "XRLXXRRLX"
输出: True
解释:
我们可以通过以下几步将start转换成end:
RXXLRXRXL ->
XRXLRXRXL ->
XRLXRXRXL ->
XRLXXRRXL ->
XRLXXRRLX

注意:

1. 1 <= len(start) = len(end) <= 10000。
2. start和end中的字符串仅限于'L', 'R'和'X'。

---

Runtime: 24 ms

Memory Usage: 19.5 MB

class Solution {
    func canTransform(_ start: String, _ end: String) -> Bool {
        var start = Array(start)
        var end = Array(end)
        var n:Int = start.count
        var cntL:Int = 0
        var cntR:Int = 0
        for i in 0..<n
        {
            if start[i] == "R" {cntR += 1}
            if end[i] == "L" {cntL += 1}
            if start[i] == "L" {cntL -= 1}
            if end[i] == "R" {cntR -= 1}
            if cntL < 0 || cntR < 0 || cntL * cntR != 0
            {
                return false
            }
        }
        return cntL == 0 && cntR == 0
    }
}

---

68ms

class Solution {
    func canTransform(_ start: String, _ end: String) -> Bool {
        let cs = Array(start)
        let ce = Array(end)
        let ts = String(cs.filter{ $0 != "X" } )
        let te = String(ce.filter{ $0 != "X" } )
                                           
        guard ts == te else { return false }
        
        var sr = [Int]()
        var sl = [Int]()
        
        for (i, char) in cs.enumerated() {
            if char == "R" {
                sr.append(i)
            } else if char == "L" {
                sl.append(i)
            }
        }
        
        var rCount = 0
        var lCount = 0
        
        for (i, char) in ce.enumerated() {
            if char == "R" {
                if sr[rCount] > i {
                    return false
                } else {
                    rCount += 1
                }
            } else if char == "L" {
                if sl[lCount] < i {
                    return false
                } else {
                    lCount += 1
                }
            }
        } 
        
        return true
    }
}

---

96ms

class Solution {    
    func compare(_ start: String, _ end: String) -> Bool {
        var rs1 = 0
        var ls1 = 0
        var xs1 = 0 
        var rs2 = 0
        var ls2 = 0
        var xs2 = 0
        for i in start.indices {
            switch start[i] {
                case "R":
                    rs1 += 1
                case "L":
                    ls1 += 1
                case "X":
                    xs1 += 1
                default:
                    break
            }
            switch end[i] {
                case "R":
                    rs2 += 1
                case "L":
                    ls2 += 1
                case "X":
                    xs2 += 1
                default:
                    break
            }
        }
        return rs1 == rs2 && ls1 == ls2 && xs1 == xs2
    }
    
    func canTransform(_ start: String, _ end: String) -> Bool {
        var rs = [String.Index]()
        var ls = [String.Index]()
        for (i, ch) in zip(start.indices, start) {
            if ch == "R" {
                rs.append(i)
            } else if ch == "L" {
                ls.append(i)
            }
        }
        rs.reverse()
        ls.reverse()
        
        if !compare(start, end) {
            return false
        }
        
        for (i, ch) in zip(end.indices, end) {
            if ch == "R" {
                if let nextRIdx = rs.last, nextRIdx <= i {
                    if let nextLIdx = ls.last {
                        if nextLIdx < nextRIdx {
                            // impossible to move R through L
                            return false
                        } else {
                            rs.removeLast()
                        }
                    } else {
                        rs.removeLast()
                    }
                } else {
                    return false
                }
            } else if ch == "L" {
                if let nextLIdx = ls.last, nextLIdx >= i {
                    if let nextRIdx = rs.last {
                        if nextRIdx < nextLIdx {
                            // impossible to move L through R
                            return false
                        } else {
                            ls.removeLast()
                        }
                    } else {
                        ls.removeLast()
                    }
                } else {
                    return false
                }
            }
        }
        return true
    }
}

---

104ms

class Solution {
    func canTransform(_ start: String, _ end: String) -> Bool {
        guard start.count >= 1 && start.count <= 10000 && end.count >= 1 && end.count <= 10000 else {
            return false
        }
        let startChars = Array(start), endChars = Array(end)
        var startInfos = [(Character, Int)](), endInfos = [(Character, Int)]()
        for (index, char) in startChars.enumerated() {
            if char == "L" || char == "R" {
                startInfos.append((char, index))
            } else if char != "X" {
                return false
            }
        }
        for (index, char) in endChars.enumerated() {
            if char == "L" || char == "R" {
                endInfos.append((char, index))
            } else if char != "X" {
                return false
            }
        }
        let startInfosChars = startInfos.map {
            $0.0
        }
        let endInfosChars = endInfos.map {
            $0.0
        }
        guard startInfosChars == endInfosChars else {
            return false
        }
        for (index, startInfo) in startInfos.enumerated() {
            let endInfo = endInfos[index]
            if startInfo.0 == "L" {
                guard startInfo.1 >= endInfo.1 else {
                    return false
                }
            } else {
                guard startInfo.1 <= endInfo.1 else {
                    return false
                }
            }
        }
        return true
    }
}