Create 0127-word-ladder.swift

Author: drxlx

swift/0127-word-ladder.swift

@@ -0,0 +1,44 @@
+class Solution {
+    func ladderLength(_ beginWord: String, _ endWord: String, _ wordList: [String]) -> Int {
+        var wordList = wordList
+        if !wordList.contains(endWord) {
+            return 0
+        }
+
+        var nei = [String: [String]]()
+        wordList.append(beginWord)
+        for word in wordList {
+            for j in 0..<word.count {
+                let pattern = word.prefix(j) + "*" + word.dropFirst(j + 1)
+                nei[String(pattern), default: []].append(word)
+            }
+        }
+
+        var visit = Set([beginWord])
+        var q = [beginWord]
+        var res = 1
+        
+        while !q.isEmpty {
+            let count = q.count
+            for _ in 0..<count {
+                let word = q.removeFirst()
+                if word == endWord {
+                    return res
+                }
+                for j in 0..<word.count {
+                    let pattern = word.prefix(j) + "*" + word.dropFirst(j + 1)
+                    if let neiWords = nei[String(pattern)] {
+                        for neiWord in neiWords {
+                            if !visit.contains(neiWord) {
+                                visit.insert(neiWord)
+                                q.append(neiWord)
+                            }
+                        }
+                    }
+                }
+            }
+            res += 1
+        }
+        return 0
+    }
+}