描述
給出兩個單詞（start和end）和一個字典，找到從start到end的最短轉(zhuǎn)換序列
比如
每次只能改變一個字母。
變換過程中的中間單詞必須在字典中出現(xiàn)此熬。
注意事項
如果沒有轉(zhuǎn)換序列則返回0甜刻。
所有單詞具有相同的長度呻袭。
所有單詞都只包含小寫字母顿天。
樣例
給出數(shù)據(jù)如下：
start = "hit"
end = "cog"
dict = ["hot","dot","dog","lot","log"]
一個最短的變換序列是 "hit" -> "hot" -> "dot" -> "dog" -> "cog"泄朴，
返回它的長度 5
代碼
- version: LintCode ( Set<String> )
public class Solution {
public int ladderLength(String start, String end, Set<String> dict) {
if (dict == null) {
return 0;
}
if (start.equals(end)) {
return 1;
}
dict.add(start);
dict.add(end);
HashSet<String> hash = new HashSet<String>();
Queue<String> queue = new LinkedList<String>();
queue.offer(start);
hash.add(start);
int length = 1;
while(!queue.isEmpty()) {
length++;
int size = queue.size();
for (int i = 0; i < size; i++) {
String word = queue.poll();
for (String nextWord: getNextWords(word, dict)) {
if (hash.contains(nextWord)) {
continue;
}
if (nextWord.equals(end)) {
return length;
}
hash.add(nextWord);
queue.offer(nextWord);
}
}
}
return 0;
}
// replace character of a string at given index to a given character
// return a new string
private String replace(String s, int index, char c) {
char[] chars = s.toCharArray();
chars[index] = c;
return new String(chars);
}
// get connections with given word.
// for example, given word = 'hot', dict = {'hot', 'hit', 'hog'}
// it will return ['hit', 'hog']
private ArrayList<String> getNextWords(String word, Set<String> dict) {
ArrayList<String> nextWords = new ArrayList<String>();
for (char c = 'a'; c <= 'z'; c++) {
for (int i = 0; i < word.length(); i++) {
if (c == word.charAt(i)) {
continue;
}
String nextWord = replace(word, i, c);
if (dict.contains(nextWord)) {
nextWords.add(nextWord);
}
}
}
return nextWords;
}
}
- version: LeetCode
public class Solution {
public int ladderLength(String start, String end, List<String> wordList) {
Set<String> dict = new HashSet<>();
for (String word : wordList) {
dict.add(word);
}
if (start.equals(end)) {
return 1;
}
HashSet<String> hash = new HashSet<String>();
Queue<String> queue = new LinkedList<String>();
queue.offer(start);
hash.add(start);
int length = 1;
while (!queue.isEmpty()) {
length++;
int size = queue.size();
for (int i = 0; i < size; i++) {
String word = queue.poll();
for (String nextWord: getNextWords(word, dict)) {
if (hash.contains(nextWord)) {
continue;
}
if (nextWord.equals(end)) {
return length;
}
hash.add(nextWord);
queue.offer(nextWord);
}
}
}
return 0;
}
// replace character of a string at given index to a given character
// return a new string
private String replace(String s, int index, char c) {
char[] chars = s.toCharArray();
chars[index] = c;
return new String(chars);
}
// get connections with given word.
// for example, given word = 'hot', dict = {'hot', 'hit', 'hog'}
// it will return ['hit', 'hog']
private ArrayList<String> getNextWords(String word, Set<String> dict) {
ArrayList<String> nextWords = new ArrayList<String>();
for (char c = 'a'; c <= 'z'; c++) {
for (int i = 0; i < word.length(); i++) {
if (c == word.charAt(i)) {
continue;
}
String nextWord = replace(word, i, c);
if (dict.contains(nextWord)) {
nextWords.add(nextWord);
}
}
}
return nextWords;
}
}
