TreeMap使用案例-多个映射(中级版)

细节问题请看简单版
public class WordMapn {
     public static Map<String, List<String>>
         computeAdjacentWords(List<String> theWords){
         Map<String, List<String>> adjWords=new TreeMap<>(); 
         //只要长度相等的单词才有可能满足条件，先按长度找出来，存在wordsByLength中
         Map<Integer,List<String>> wordsByLength=new TreeMap<>();
         for(String w:theWords){
             update(wordsByLength,w.length(),w);
         }
         //对于每种长度的单词，只要进行内部查找就可以了
         for(List<String> groupsWords:wordsByLength.values()){
             String[] words=new String[groupsWords.size()];
             groupsWords.toArray(words);
             for(int i=0;i<words.length;i++){
                 for(int j=i+1;j<words.length;j++){
                     if(oneCharOff(words[i],words[j])){
                     update(adjWords,words[i],words[j]);
                     update(adjWords,words[j],words[i]);
                     }
                 }
             }
         }
         return adjWords;
     }
     private static <KeyType> void update(Map<KeyType, List<String>> m,
                                 KeyType key,String value){
         List<String> lst=m.get(key);
         if(lst==null){
             lst=new ArrayList<>();
             m.put(key, lst);
         }
         lst.add(value);
     }
     //检测两个单词时候只在一个字母上不同
     private static boolean oneCharOff(String word1,String word2){
         if(word1.length()!=word2.length()){
             return false;
         }
         int diffs=0;
         for(int i=0;i<word1.length();i++){
             if(word1.charAt(i)!=word2.charAt(i)){
                 if(++diffs>1){
                     return false;
                 }
             }
         }
         return diffs==1;
     }
 }测试：
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         List<String> list=null;
         String[] a=new String[]{"dine","line","mine","pine","vine","wide","wife","wipe","wire"};
         list=Arrays.asList(a);
         Map<String,List<String>> m=WordMapn.computeAdjacentWords(list);
         for(Map.Entry<String,List<String>> me : m.entrySet()) {

            System.out.println(me.getKey() + ": " + me.getValue());

         }效果：
dine: [line, mine, pine, vine]
 line: [dine, mine, pine, vine]
 mine: [dine, line, pine, vine]
 pine: [dine, line, mine, vine]
 vine: [dine, line, mine, pine]
 wide: [wife, wipe, wire]
 wife: [wide, wipe, wire]
 wipe: [wide, wife, wire]
 wire: [wide, wife, wipe]