leetcode：Word Ladder

广度优先搜索，求出从源字符串到目标字符串的变换过程，每一步变换只能是更改其中一个字符串

public class Solution {    public int ladderLength(String start, String end, HashSet<String> dict) {         if (dict.size() == 0)              return 0;          LinkedList<String> wordQueue = new LinkedList<String>();        LinkedList<Integer> distanceQueue = new LinkedList<Integer>();         wordQueue.add(start);        distanceQueue.add(1);          while(!wordQueue.isEmpty()){            String currWord = wordQueue.pop();            Integer currDistance = distanceQueue.pop();             if(currWord.equals(end)){                return currDistance;            }             for(int i=0; i<currWord.length(); i++){                char[] currCharArr = currWord.toCharArray();                for(char c='a'; c<='z'; c++){                    currCharArr[i] = c;                     String newWord = new String(currCharArr);                    if(dict.contains(newWord)){                        wordQueue.add(newWord);                        distanceQueue.add(currDistance+1);                        dict.remove(newWord);                    }                }            }        }         return 0;    }}