127 copy fastest

Author: aQua

Algorithms/0127.word-ladder/word-ladder.go

@@ -1,78 +1,77 @@
 package Problem0127
 
 func ladderLength(beginWord string, endWord string, words []string) int {
+	dictMap := make(map[string]byte)
 
-	// isTransedEndWord 用于在生成 trans 的过程中标记，存在 ->endWord 的转换关系
-	// 用于提前结束
-	isTransedEndWord := false
-	// cnt 用于记录生成trans的迭代次数
-	// 其实也是最短路径的长度
-	res := 1
-	var bfs func([]string, []string)
-	// 使用 bfs 方法，递归地生成 trans
-	bfs = func(words, nodes []string) {
-		res++
-		// words 中的 w
-		//     与 nodes 中的 n ，可以实现 n->w 的转换，
-		//       则，w 会被放入 newNodes
-		//     否则，w 会被放入 newWords
-		newWords := make([]string, 0, len(words))
-		newNodes := make([]string, 0, len(words))
-		for _, w := range words {
-			isTransed := false
-			for _, n := range nodes {
-				if isTransable(n, w) {
-					isTransed = true
+	for i := 0; i < len(words); i++ {
+		if _, ok := dictMap[words[i]]; !ok {
+			dictMap[words[i]] = byte(1)
+		}
+	}
 
-				}
-			}
+	var wq wordQueue
+	dist := 2
 
-			if isTransed {
-				if w == endWord {
-					isTransedEndWord = true
-					return
-				}
-				newNodes = append(newNodes, w)
-			} else {
-				newWords = append(newWords, w)
+	addNextWords(beginWord, dictMap, &wq)
+	for !wq.empty() {
+		wqLen := wq.size()
+		for i := 0; i < wqLen; i++ {
+			word := wq.popNext()
+			if word == endWord {
+				return dist
 			}
-		}
 
-		if len(newWords) == 0 || // words 的所有单词都已经可以从 beginWord trans 到
-			len(newNodes) == 0 { // newWords 中单词，是 beginWord 无法 trans 到的
-			return
+			addNextWords(word, dictMap, &wq)
 		}
-
-		// 上面没有 return，要继续完善 trans
-		bfs(newWords, newNodes)
+		dist++
 	}
 
-	// 第一代 nodes 含有且仅含有 beginWord
-	nodes := []string{beginWord}
-	bfs(words, nodes)
+	return 0
+}
+
+func addNextWords(beginWord string, dictMap map[string]byte, wq *wordQueue) {
+	bytes := []byte(beginWord)
+	delete(dictMap, beginWord)
+	for i := 0; i < len(bytes); i++ {
+		diffLetter := bytes[i]
+		for j := 0; j < 26; j++ {
+			b := 'a' + byte(j)
+			if b == diffLetter {
+				continue
+			}
 
-	if !isTransedEndWord {
-		// beginWord 无法 trans 到 endWord
-		return 0
+			bytes[i] = b
+			if _, ok := dictMap[string(bytes)]; ok {
+				wq.push(string(bytes))
+				delete(dictMap, string(bytes))
+			}
+		}
+		bytes[i] = diffLetter
 	}
+}
 
-	return res
+type wordQueue struct {
+	words []string
 }
 
-func isTransable(a, b string) bool {
-	if a == b {
-		return false
-	}
-	// onceAgain == true 说明已经出现过不同的字符了
-	onceAgain := false
-	for i := range a {
-		if a[i] != b[i] {
-			if onceAgain {
-				return false
-			}
-			onceAgain = true
-		}
+func (wq *wordQueue) empty() bool {
+	return len(wq.words) == 0
+}
+
+func (wq *wordQueue) popNext() string {
+	if len(wq.words) == 0 {
+		return ""
 	}
 
-	return true
+	s := wq.words[0]
+	wq.words = wq.words[1:]
+	return s
+}
+
+func (wq *wordQueue) push(s string) {
+	wq.words = append(wq.words, s)
+}
+
+func (wq *wordQueue) size() int {
+	return len(wq.words)
 }