10-4 字典树的前缀查询

前缀查询:查询字典树中是否存在以指定字符串为前缀的单词！

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mport java.util.TreeMap;   public class Trie {       private class Node{           public boolean isWord;         public TreeMap<Character, Node> next;           public Node(boolean isWord){             this.isWord = isWord;             next = new TreeMap<>();         }           public Node(){             this(false);         }     }       private Node root;     private int size;       public Trie(){         root = new Node();         size = 0;     }       // 获得Trie中存储的单词数量     public int getSize(){         return size;     }       // 向Trie中添加一个新的单词word     public void add(String word){           Node cur = root;         for(int i = 0 ; i < word.length() ; i ++){             char c = word.charAt(i);             if(cur.next.get(c) == null)                 cur.next.put(c, new Node());             cur = cur.next.get(c);         }           if(!cur.isWord){             cur.isWord = true;             size ++;         }     }       // 查询单词word是否在Trie中     public boolean contains(String word){           Node cur = root;         for(int i = 0 ; i < word.length() ; i ++){             char c = word.charAt(i);             if(cur.next.get(c) == null)                 return false;             cur = cur.next.get(c);         }         return cur.isWord;     }       // 查询是否在Trie中有单词以prefix为前缀     // 前缀:一个单词的前若干个字母组成的串称为这个单词的一个前缀，整合单词也是这个单词本身的一个前缀     // 前缀查询和contains查询逻辑相似     public boolean isPrefix(String prefix){           Node cur = root;         for(int i = 0 ; i < prefix.length() ; i ++){             char c = prefix.charAt(i);             if(cur.next.get(c) == null)                 return false;             cur = cur.next.get(c);         }           return true;     } }