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WordLadder.java
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WordLadder.java
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package Leetcode;
import java.util.*;
/**
* @author kalpak
*
* A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words such that:
*
* The first word in the sequence is beginWord.
* The last word in the sequence is endWord.
* Only one letter is different between each adjacent pair of words in the sequence.
* Every word in the sequence is in wordList.
* Given two words, beginWord and endWord, and a dictionary wordList,
* return the number of words in the shortest transformation sequence from beginWord to endWord, or 0 if no such sequence exists.
*
*
* Example 1:
* Input: beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log","cog"]
* Output: 5
* Explanation: One shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog" with 5 words.
*
*
* Example 2:
* Input: beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log"]
* Output: 0
* Explanation: The endWord "cog" is not in wordList, therefore there is no possible transformation.
*
*
* Constraints:
*
* 1 <= beginWord.length <= 10
* endWord.length == beginWord.length
* 1 <= wordList.length <= 5000
* wordList[i].length == beginWord.length
* beginWord, endWord, and wordList[i] consist of lowercase English letters.
* beginWord != endWord
* All the strings in wordList are unique.
*
*/
public class WordLadder {
public static int ladderLength(String beginWord, String endWord, List<String> wordList) {
Set<String> givenDictionary = new HashSet<>(wordList);
Queue<String> queue = new LinkedList<>();
Set<String> visited = new HashSet<>();
int level = 0;
queue.offer(beginWord);
visited.add(beginWord);
while(!queue.isEmpty()) {
int size = queue.size();
while(size > 0) {
String word = queue.poll();
// check if word is the destination word
if(word.equals(endWord))
return level + 1;
// Generate all permutations of the word by changing each character from [a-z]
char[] temp = word.toCharArray();
// for each position
for(int i = 0; i < temp.length; i++) {
char backup = temp[i];
// check from [a-z]
for(char ch = 'a'; ch <= 'z'; ch++) {
temp[i] = ch;
String nextWord = String.valueOf(temp);
if(!visited.contains(nextWord) && givenDictionary.contains(nextWord)) {
queue.add(nextWord);
visited.add(nextWord);
}
}
temp[i] = backup;
}
size--;
}
level++;
}
return 0;
}
public static void main(String[] args) {
List<String> wordList = new ArrayList<>(Arrays.asList(new String[]{"hot","dot","dog","lot","log","cog"}));
System.out.println("The number of words in the shortest transformation is : " + ladderLength("hit", "cog", wordList));
}
}