package Strings;

import java.util.List;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.Queue;
import java.util.HashSet;

/*
 **Problem Statement:**
 A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that:

 Every adjacent pair of words differs by a single letter.
 Every si for 1 <= i <= k is in wordList. Note that beginWord does not need to be in wordList.
 sk == endWord
 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 sequence is "hit" -> "hot" -> "dot" -> "dog" -> cog", which is 5 words long.

 **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 valid transformation sequence.

 **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 words in wordList are unique.
*/

class WordLadder {

 /** Driver Code */
 public static void main(String []args){

 String beginWord = "hit";
 String endWord = "cog";
 String words[] = {"hot","dot","dog","lot","log","cog"}; 
 List<String> wordList = Arrays.asList(words);

 System.out.println("Ladder Length: " + ladderLength(beginWord,endWord,wordList));
 }

 /**
 * This function finds the ladderLength
 * @param beginWord: Starting word of the ladder 
 * @param endWord: Ending word of the ladder
 * @param wordList: This list contains the words which needs to be included in ladder.
 * @return ladderLength: This function will return the ladderLength(level) if the endword is there. 
 * Otherwise, will return the length as 0.
 */

 public static int ladderLength(String beginWord, String endWord, List<String> wordList) {
 HashSet<String> set = new HashSet();
 for(String word : wordList){
 set.add(word);
 }
 
 if(!set.contains(endWord)) return 0;
 
 Queue<String> queue = new LinkedList();
 queue.offer(beginWord);
 int level = 1;
 
 while(!queue.isEmpty()){
 int size = queue.size();
 for(int i = 0; i < size; i++){
 String curr = queue.poll();
 char[] words_chars = curr.toCharArray();
 for(int j = 0; j < words_chars.length; j++){
 char original_chars = words_chars[j];
 for(char c = 'a'; c <= 'z'; c++){
 if(words_chars[j] == c) continue;
 words_chars[j] = c;
 String new_word = String.valueOf(words_chars);
 if(new_word.equals(endWord)) return level+1;
 if(set.contains(new_word)){
 set.remove(new_word);
 queue.offer(new_word);
 }
 }
 words_chars[j] = original_chars;
 }
 }
 level++;
 }
 return 0;
 }
}