Middle-题目119：127. Word Ladder

题目原文：
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 intermediate word must exist in the word list
For example,
Given:
beginWord = “hit”
endWord = “cog”
wordList = [“hot”,”dot”,”dog”,”lot”,”log”]
As one shortest transformation is “hit” -> “hot” -> “dot” -> “dog” -> “cog”,
return its length 5.
题目大意：
给出两个单词beginWord和endWord，和一个字典，求出从beginWord到endWord的最短转换序列，要求中间单词必须是字典中的，且每次只能转换一个字母。
题目分析：
表面上看是一个单源最短路径问题，博客中说这道题的test case和题目要求都有问题，所以我也就没做，以下只贴出ac代码。
源码：（language：java）

public class Solution {

    public int ladderLength(String beginWord, String endWord, Set<String> wordList) {
        Set<String> beginSet = new HashSet<String>(), endSet = new HashSet<String>();

        int len = 1;
        int strLen = beginWord.length();
        HashSet<String> visited = new HashSet<String>();

        beginSet.add(beginWord);
        endSet.add(endWord);
        while (!beginSet.isEmpty() && !endSet.isEmpty()) {
            if (beginSet.size() > endSet.size()) {
                Set<String> set = beginSet;
                beginSet = endSet;
                endSet = set;
            }

            Set<String> temp = new HashSet<String>();
            for (String word : beginSet) {
                char[] chs = word.toCharArray();

                for (int i = 0; i < chs.length; i++) {
                    for (char c = 'a'; c <= 'z'; c++) {
                        char old = chs[i];
                        chs[i] = c;
                        String target = String.valueOf(chs);

                        if (endSet.contains(target)) {
                            return len + 1;
                        }

                        if (!visited.contains(target) && wordList.contains(target)) {
                            temp.add(target);
                            visited.add(target);
                        }
                        chs[i] = old;
                    }
                }
            }

            beginSet = temp;
            len++;
        }

        return 0;
    }
}

成绩：
47ms,beats 89.34%,众数97ms,2.42%
Cmershen的碎碎念：
据说后面的word ladder 2这道题也是有问题的。