_0127_WordLadder.java

package com.diguage.algorithm.leetcode;

import java.util.*;

/**
 * = 127. Word Ladder
 *
 * https://leetcode.com/problems/word-ladder/[Word Ladder - LeetCode]
 *
 * Given two words (beginWord and endWord), and a dictionary's word list, find the length of shortest transformation sequence from beginWord to endWord, such that:
 *
 * . Only one letter can be changed at a time.
 * . Each transformed word must exist in the word list. Note that beginWord is not a transformed word.
 *
 * *Note:*
 *
 * * Return 0 if there is no such transformation sequence.
 * * All words have the same length.
 * * All words contain only lowercase alphabetic characters.
 * * You may assume no duplicates in the word list.
 * * You may assume beginWord and endWord are non-empty and are not the same.
 *
 * .Example 2:
 * [source]
 * ----
 * Input:
 * beginWord = "hit",
 * endWord = "cog",
 * wordList = ["hot","dot","dog","lot","log","cog"]
 *
 * Output: 5
 *
 * Explanation: As one shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog",
 * return its length 5.
 * ----
 *
 * .Example 2:
 * [source]
 * ----
 * Input:
 * beginWord = "hit"
 * endWord = "cog"
 * wordList = ["hot","dot","dog","lot","log"]
 *
 * Output: 0
 *
 * Explanation: The endWord "cog" is not in wordList, therefore no possible transformation.
 * ----
 *
 * @author D瓜哥, https://www.diguage.com/
 * @since 2020-01-25 18:43
 */
public class _0127_WordLadder {
    /**
     * Runtime: 43 ms, faster than 80.36% of Java online submissions for Word Ladder.
     *
     * Memory Usage: 49.1 MB, less than 5.11% of Java online submissions for Word Ladder.
     *
     * Copy from: https://leetcode.com/problems/word-ladder/solution/[Word Ladder solution - LeetCode]
     */
    public int ladderLength(String beginWord, String endWord, List<String> wordList) {
        int L = beginWord.length();
        Map<String, List<String>> allComboDict = new HashMap<>();
        wordList.forEach(word -> {
            for (int i = 0; i < L; i++) {
                String newWord = word.substring(0, i) + "*" + word.substring(i + 1, L);
                List<String> transformations = allComboDict.getOrDefault(newWord, new ArrayList<>());
                transformations.add(word);
                allComboDict.put(newWord, transformations);
            }
        });

        Queue<Pair<String, Integer>> Q = new LinkedList<>();
        Q.add(new Pair<>(beginWord, 1));
        Map<String, Boolean> visited = new HashMap<>();
        visited.put(beginWord, true);

        while (!Q.isEmpty()) {
            Pair<String, Integer> node = Q.remove();
            String word = node.getKey();
            Integer level = node.getValue();
            for (int i = 0; i < L; i++) {
                String newWord = word.substring(0, i) + "*" + word.substring(i + 1, L);
                for (String adjacentWord : allComboDict.getOrDefault(newWord, Collections.emptyList())) {
                    if (adjacentWord.equals(endWord)) {
                        return level + 1;
                    }
                    if (!visited.containsKey(adjacentWord)) {
                        visited.put(adjacentWord, true);
                        Q.add(new Pair<>(adjacentWord, level + 1));
                    }
                }
            }
        }

        return 0;
    }

    public static class Pair<K, V> {
        private K key;
        private V value;

        public Pair(K key, V value) {

        }

        public K getKey() {
            return key;
        }

        public void setKey(K key) {
            this.key = key;
        }

        public V getValue() {
            return value;
        }

        public void setValue(V value) {
            this.value = value;
        }
    }

    public static void main(String[] args) {
        _0127_WordLadder solution = new _0127_WordLadder();
        int r1 = solution.ladderLength("hit", "cog", Arrays.asList("hot", "dot", "dog", "lot", "log", "cog"));
        System.out.println((r1 == 5) + " : " + r1);
    }
}