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| 1 | +package com.leetcode.graphs; |
| 2 | + |
| 3 | + |
| 4 | +import javafx.util.Pair; |
| 5 | + |
| 6 | +import java.util.*; |
| 7 | + |
| 8 | +import static org.junit.jupiter.api.Assertions.assertEquals; |
| 9 | + |
| 10 | +/** |
| 11 | + * Level: Medium |
| 12 | + * Link: https://leetcode.com/problems/word-ladder/ |
| 13 | + * Description: |
| 14 | + * Given two words (beginWord and endWord), and a dictionary's word list, find the length of shortest transformation |
| 15 | + * sequence from beginWord to endWord, such that: |
| 16 | + * <p> |
| 17 | + * Only one letter can be changed at a time. Each transformed word must exist in the word list. Note that beginWord |
| 18 | + * is not a transformed word. |
| 19 | + * <p> |
| 20 | + * Note: |
| 21 | + * - Return 0 if there is no such transformation sequence. |
| 22 | + * - All words have the same length. |
| 23 | + * - All words contain only lowercase alphabetic characters. |
| 24 | + * - You may assume no duplicates in the word list. |
| 25 | + * - You may assume beginWord and endWord are non-empty and are not the same. |
| 26 | + * <p> |
| 27 | + * Example 1: |
| 28 | + * Input: |
| 29 | + * beginWord = "hit", |
| 30 | + * endWord = "cog", |
| 31 | + * wordList = ["hot","dot","dog","lot","log","cog"] |
| 32 | + * <p> |
| 33 | + * Output: 5 |
| 34 | + * <p> |
| 35 | + * Explanation: As one shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog", |
| 36 | + * return its length 5. |
| 37 | + * <p> |
| 38 | + * Example 2: |
| 39 | + * Input: |
| 40 | + * beginWord = "hit" |
| 41 | + * endWord = "cog" |
| 42 | + * wordList = ["hot","dot","dog","lot","log"] |
| 43 | + * <p> |
| 44 | + * Output: 0 |
| 45 | + * <p> |
| 46 | + * Explanation: The endWord "cog" is not in wordList, therefore no possible transformation. |
| 47 | + * |
| 48 | + * @author rampatra |
| 49 | + * @since 2019年08月15日 |
| 50 | + */ |
| 51 | +public class WordLadder { |
| 52 | + |
| 53 | + /** |
| 54 | + * Runtime: <a href="https://leetcode.com/submissions/detail/251953011/">78 ms</a>. |
| 55 | + * |
| 56 | + * @param beginWord |
| 57 | + * @param endWord |
| 58 | + * @param wordList |
| 59 | + * @return |
| 60 | + */ |
| 61 | + public static int ladderLength(String beginWord, String endWord, List<String> wordList) { |
| 62 | + int L = beginWord.length(); |
| 63 | + Map<String, Set<String>> originalToTransformedWordMap = new HashMap<>(); |
| 64 | + Queue<Pair<String, Integer>> queue = new LinkedList<>(); |
| 65 | + |
| 66 | + wordList.forEach(word -> { |
| 67 | + String transformedWord; |
| 68 | + for (int i = 0; i < L; i++) { |
| 69 | + transformedWord = word.substring(0, i) + "*" + word.substring(i + 1, L); |
| 70 | + originalToTransformedWordMap.putIfAbsent(transformedWord, new HashSet<>()); |
| 71 | + originalToTransformedWordMap.get(transformedWord).add(word); |
| 72 | + } |
| 73 | + } |
| 74 | + ); |
| 75 | + |
| 76 | + Set<String> visited = new HashSet<>(); |
| 77 | + queue.add(new Pair<>(beginWord, 1)); |
| 78 | + visited.add(beginWord); |
| 79 | + |
| 80 | + while (!queue.isEmpty()) { |
| 81 | + Pair<String, Integer> currPair = queue.poll(); |
| 82 | + String word = currPair.getKey(); |
| 83 | + Integer level = currPair.getValue(); |
| 84 | + |
| 85 | + if (word.equals(endWord)) { |
| 86 | + return level; |
| 87 | + } |
| 88 | + |
| 89 | + String transformedWord; |
| 90 | + for (int i = 0; i < L; i++) { |
| 91 | + transformedWord = word.substring(0, i) + "*" + word.substring(i + 1, L); |
| 92 | + |
| 93 | + for (String originalWord : originalToTransformedWordMap.getOrDefault(transformedWord, Collections.emptySet())) { |
| 94 | + if (!visited.contains(originalWord)) { |
| 95 | + queue.add(new Pair<>(originalWord, level + 1)); |
| 96 | + visited.add(originalWord); |
| 97 | + } |
| 98 | + } |
| 99 | + } |
| 100 | + } |
| 101 | + |
| 102 | + return 0; |
| 103 | + } |
| 104 | + |
| 105 | + public static void main(String[] args) { |
| 106 | + assertEquals(5, ladderLength("hit", "cog", Arrays.asList("hot", "dot", "dog", "lot", "log", "cog"))); |
| 107 | + assertEquals(0, ladderLength("hit", "cog", Arrays.asList("hot", "dot", "dog", "lot", "log"))); |
| 108 | + } |
| 109 | +} |
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