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word-ladder.java
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word-ladder.java
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// 127. 单词接龙 - Hard
// https://leetcode-cn.com/problems/word-ladder/
package java;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
import java.util.Set;
class WordLadder {
/**
* BFS题,可以使用双向BFS优化时间
*/
public int ladderLength(String beginWord, String endWord, List<String> wordList) {
Set<String> visited = new HashSet<>();
Queue<String> q = new LinkedList<>();
q.offer(beginWord);
int count = 0;
while (!q.isEmpty()) {
int size = q.size();
for (int i = 0; i < size; i++) {
String str = q.poll();
if (str.equals(endWord)) return count + 1;
for (String word : wordList) {
if (visited.contains(word)) continue;
if (convertable(str, word)) {
q.offer(word);
visited.add(word);
}
}
}
count++;
}
return 0;
}
private boolean convertable(String word1, String word2) {
int diff = 0;
for (int i = 0; i < word1.length(); i++) {
if (diff > 1) {
return false;
}
if (word1.charAt(i) != word2.charAt(i)) {
diff++;
}
}
return diff == 1;
}
}