Word Ladder

import java.util.*;

class Solution {
    public int ladderLength(String beginWord, String endWord, List<String> wordList) {
        Set<String> dict = new HashSet<>(wordList);
        if (!dict.contains(endWord)) return 0;
        Deque<String> q = new ArrayDeque<>();
        q.offer(beginWord);
        dict.remove(beginWord);
        for (int len = 1; !q.isEmpty(); len++) {
            for (int size = q.size(); size > 0; size--) {
                String w = q.poll();
                if (w.equals(endWord)) return len;
                char[] c = w.toCharArray();
                for (int i = 0; i < c.length; i++) {
                    char orig = c[i];
                    for (char ch = 'a'; ch <= 'z'; ch++) {
                        if (ch == orig) continue;
                        c[i] = ch;
                        String t = new String(c);
                        if (dict.remove(t)) q.offer(t);
                    }
                    c[i] = orig;
                }
            }
        }
        return 0;
    }
}