feat: add swift implementation to lcof2 problem: No.108 (#3621)

Author: klever34

lcof2/剑指 Offer II 108. 单词演变/README.md

@@ -204,6 +204,43 @@ func ladderLength(beginWord string, endWord string, wordList []string) int {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func ladderLength(_ beginWord: String, _ endWord: String, _ wordList: [String]) -> Int {
+        var words = Set(wordList)
+        var queue = [beginWord]
+        var ans = 1
+
+        while !queue.isEmpty {
+            for _ in 0..<queue.count {
+                let s = queue.removeFirst()
+                var chars = Array(s)
+                for j in 0..<chars.count {
+                    let ch = chars[j]
+                    for k in 0..<26 {
+                        chars[j] = Character(UnicodeScalar(k + 97)!)
+                        let t = String(chars)
+                        if !words.contains(t) {
+                            continue
+                        }
+                        if t == endWord {
+                            return ans + 1
+                        }
+                        queue.append(t)
+                        words.remove(t)
+                    }
+                    chars[j] = ch
+                }
+            }
+            ans += 1
+        }
+        return 0
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof2/剑指 Offer II 108. 单词演变/Solution.swift

@@ -0,0 +1,32 @@
+class Solution {
+    func ladderLength(_ beginWord: String, _ endWord: String, _ wordList: [String]) -> Int {
+        var words = Set(wordList)
+        var queue = [beginWord]
+        var ans = 1
+        
+        while !queue.isEmpty {
+            for _ in 0..<queue.count {
+                let s = queue.removeFirst()
+                var chars = Array(s)
+                for j in 0..<chars.count {
+                    let ch = chars[j]
+                    for k in 0..<26 {
+                        chars[j] = Character(UnicodeScalar(k + 97)!)
+                        let t = String(chars)
+                        if !words.contains(t) {
+                            continue
+                        }
+                        if t == endWord {
+                            return ans + 1
+                        }
+                        queue.append(t)
+                        words.remove(t)
+                    }
+                    chars[j] = ch
+                }
+            }
+            ans += 1
+        }
+        return 0
+    }
+}