feat: add swift implementation to lcci problem: No.17.22 (doocs#2817)

Author: klever34

lcci/17.22.Word Transformer/README.md

@@ -257,6 +257,58 @@ function findLadders(beginWord: string, endWord: string, wordList: string[]): st
 }
 ```
 
+```swift
+class Solution {
+    private var ans: [String] = []
+    private var wordList: [String] = []
+    private var endWord: String = ""
+    private var vis: [Bool] = []
+    
+    func findLadders(_ beginWord: String, _ endWord: String, _ wordList: [String]) -> [String] {
+        self.wordList = wordList
+        self.endWord = endWord
+        ans.append(beginWord)
+        vis = Array(repeating: false, count: wordList.count)
+        return dfs(beginWord) ? ans : []
+    }
+    
+    private func dfs(_ s: String) -> Bool {
+        if s == endWord {
+            return true
+        }
+        for i in 0..<wordList.count {
+            let t = wordList[i]
+            if vis[i] || !check(s, t) {
+                continue
+            }
+            vis[i] = true
+            ans.append(t)
+            if dfs(t) {
+                return true
+            }
+            ans.removeLast()
+        }
+        return false
+    }
+    
+    private func check(_ s: String, _ t: String) -> Bool {
+        if s.count != t.count {
+            return false
+        }
+        var cnt = 0
+        for (sc, tc) in zip(s, t) {
+            if sc != tc {
+                cnt += 1
+                if cnt > 1 {
+                    return false
+                }
+            }
+        }
+        return cnt == 1
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/17.22.Word Transformer/README_EN.md

@@ -274,6 +274,58 @@ function findLadders(beginWord: string, endWord: string, wordList: string[]): st
 }
 ```
 
+```swift
+class Solution {
+    private var ans: [String] = []
+    private var wordList: [String] = []
+    private var endWord: String = ""
+    private var vis: [Bool] = []
+    
+    func findLadders(_ beginWord: String, _ endWord: String, _ wordList: [String]) -> [String] {
+        self.wordList = wordList
+        self.endWord = endWord
+        ans.append(beginWord)
+        vis = Array(repeating: false, count: wordList.count)
+        return dfs(beginWord) ? ans : []
+    }
+    
+    private func dfs(_ s: String) -> Bool {
+        if s == endWord {
+            return true
+        }
+        for i in 0..<wordList.count {
+            let t = wordList[i]
+            if vis[i] || !check(s, t) {
+                continue
+            }
+            vis[i] = true
+            ans.append(t)
+            if dfs(t) {
+                return true
+            }
+            ans.removeLast()
+        }
+        return false
+    }
+    
+    private func check(_ s: String, _ t: String) -> Bool {
+        if s.count != t.count {
+            return false
+        }
+        var cnt = 0
+        for (sc, tc) in zip(s, t) {
+            if sc != tc {
+                cnt += 1
+                if cnt > 1 {
+                    return false
+                }
+            }
+        }
+        return cnt == 1
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/17.22.Word Transformer/Solution.swift

@@ -0,0 +1,49 @@
+class Solution {
+    private var ans: [String] = []
+    private var wordList: [String] = []
+    private var endWord: String = ""
+    private var vis: [Bool] = []
+    
+    func findLadders(_ beginWord: String, _ endWord: String, _ wordList: [String]) -> [String] {
+        self.wordList = wordList
+        self.endWord = endWord
+        ans.append(beginWord)
+        vis = Array(repeating: false, count: wordList.count)
+        return dfs(beginWord) ? ans : []
+    }
+    
+    private func dfs(_ s: String) -> Bool {
+        if s == endWord {
+            return true
+        }
+        for i in 0..<wordList.count {
+            let t = wordList[i]
+            if vis[i] || !check(s, t) {
+                continue
+            }
+            vis[i] = true
+            ans.append(t)
+            if dfs(t) {
+                return true
+            }
+            ans.removeLast()
+        }
+        return false
+    }
+    
+    private func check(_ s: String, _ t: String) -> Bool {
+        if s.count != t.count {
+            return false
+        }
+        var cnt = 0
+        for (sc, tc) in zip(s, t) {
+            if sc != tc {
+                cnt += 1
+                if cnt > 1 {
+                    return false
+                }
+            }
+        }
+        return cnt == 1
+    }
+}