add word-ladder

Author: freefcw

go/word-ladder.go

@@ -0,0 +1,90 @@
+package leetcode
+
+var (
+	llWordRelation WordRelation
+	llVisited      map[string]bool
+)
+
+type WordRelation map[string][]string
+
+func (wr WordRelation) AddRelate(word, relation string) {
+	entry, ok := wr[word]
+	if !ok {
+		entry = make([]string, 0, 8)
+	}
+	entry = append(entry, relation)
+	wr[word] = entry
+}
+
+func (wr WordRelation) GetRelate(word string) ([]string, bool) {
+	entry, ok := wr[word]
+
+	return entry, ok
+}
+
+func isLadder(s1, s2 string) bool {
+	diff := 0
+	for i := 0; i < len(s1); i++ {
+		if s1[i] != s2[i] {
+			diff++
+		}
+		if diff > 1 {
+			return false
+		}
+	}
+
+	return true
+}
+
+func bfs(beginWord, endWord string, pendingWords []string, level int) int {
+	// fmt.Printf("level %d, pending %v\n", level, pendingWords)
+	if len(pendingWords) == 0 {
+		return 0
+	}
+	newPendingWords := make([]string, 0, len(pendingWords))
+	for i := 0; i < len(pendingWords); i++ {
+		if pendingWords[i] == endWord {
+			return level + 2
+		}
+		llVisited[pendingWords[i]] = true
+		entries, ok := llWordRelation.GetRelate(pendingWords[i])
+		if !ok {
+			continue
+		}
+		for _, word := range entries {
+			if llVisited[word] {
+				continue
+			}
+			newPendingWords = append(newPendingWords, word)
+		}
+	}
+	return bfs(beginWord, endWord, newPendingWords, level+1)
+}
+
+func ladderLength(beginWord string, endWord string, wordList []string) int {
+	llWordRelation = make(WordRelation)
+	pendingWords := make([]string, 0, 8)
+	endInWordList := false
+	for i := 0; i < len(wordList); i++ {
+		if wordList[i] == endWord {
+			endInWordList = true
+		}
+
+		for j := i + 1; j < len(wordList); j++ {
+			if isLadder(wordList[i], wordList[j]) {
+				llWordRelation.AddRelate(wordList[i], wordList[j])
+				llWordRelation.AddRelate(wordList[j], wordList[i])
+			}
+		}
+		if isLadder(beginWord, wordList[i]) {
+			pendingWords = append(pendingWords, wordList[i])
+		}
+	}
+	if !endInWordList {
+		return 0
+	}
+
+	llVisited = make(map[string]bool)
+
+	return bfs(beginWord, endWord, pendingWords, 0)
+}

go/word-ladder_test.go

@@ -0,0 +1,35 @@
+package leetcode
+
+import "testing"
+
+func TestLadderLength(t *testing.T) {
+	tests := []struct {
+		beginWord string
+		endWord   string
+		words     []string
+		expect    int
+	}{
+		{
+			beginWord: "hit",
+			endWord:   "cog",
+			words:     []string{"hot", "dot", "dog", "lot", "log", "cog"},
+			expect:    5,
+		}, {
+			beginWord: "hit",
+			endWord:   "cog",
+			words:     []string{"hot", "dot", "dog", "lot", "log"},
+			expect:    0,
+		}, {
+			beginWord: "a",
+			endWord:   "c",
+			words:     []string{"a", "b", "c"},
+			expect:    2,
+		},
+	}
+	for i, item := range tests {
+		actual := ladderLength(item.beginWord, item.endWord, item.words)
+		if actual != item.expect {
+			t.Fatalf("%d expect %d actual %d\n", i, item.expect, actual)
+		}
+	}
+}