Java/src/main/java/com/thealgorithms/strings/WordLadder.java at master · tyb/Java · GitHub

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package com.thealgorithms.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;

}

Java/src/main/java/com/thealgorithms/strings/WordLadder.java at master · tyb/Java · GitHub

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