字典树 trie

  1 public class Trie {
  2     //字典树子节点最多值,任意一个单词都是由，26个字母组成的
  3     private int SIZE = 26;
  4     //根节点
  5     private TrieNode root;
  6     //初始化字典树
  7     public Trie() {
  8         root = new TrieNode();
  9     }
 10     
 11     //字典树节点
 12     private class TrieNode{
 13         //存放子节点的数组
 14         private TrieNode[] sonNode;
 15         //是否是最后一个节点
 16         private boolean isEnd;
 17         //节点的值
 18         private char val;
 19         //有多少个单词通过这个节点，即节点字符出现的次数
 20         private int num;
 21         TrieNode(){
 22             num = 1;
 23             sonNode = new TrieNode[SIZE];
 24             isEnd = false;
 25         }
 26     }
 27     
 28     //方法，建立字典树,在字典树中插入一个单词
 29     public void insert(String str){
 30         if(str == null || str.length() == 0){
 31             return ;
 32         }
 33         
 34         //获得字典树
 35         TrieNode node = root;
 36         //把字符串转换成字符数组
 37         char[] letters = str.toCharArray();
 38         //遍历字符数组，将其插入字典树中
 39         for(int i=0; i < letters.length ; i++){
 40             int pos = letters[i] - ‘a‘;
 41             if(node.sonNode[pos] == null){
 42                 node.sonNode[pos] = new TrieNode();
 43                 node.sonNode[pos].val = letters[i];
 44             }else{
 45                 node.sonNode[pos].num++;
 46             }
 47             node = node.sonNode[pos];
 48         }
 49         node.isEnd = true;
 50     }
 51     
 52     //计算单词前缀的数量
 53     public int countPrefix(String prefix){
 54         if(prefix == null || prefix.length() == 0){
 55             return -1;
 56         }
 57         //得到字典树
 58         TrieNode node = root;
 59         char[] letters = prefix.toCharArray();
 60         for(int i = 0 , len = letters.length; i < len; i++){
 61             int pos = letters[i] - ‘a‘;
 62             if(node.sonNode[pos] == null){
 63                 return 0;
 64             }else{
 65                 node = node.sonNode[pos];
 66             }
 67         }
 68         return node.num;
 69     }
 70     
 71     //在字典树中查找一个完全匹配的单词
 72     public boolean has(String str){
 73         if(str == null || str.length() == 0){
 74             return false;
 75         }
 76         //得到字典树
 77         TrieNode node = root;
 78         char[] letters = str.toCharArray();
 79         for(int i = 0, len = str.length(); i < len; i++){
 80             int pos = letters[i] - ‘a‘;
 81             if(node.sonNode[pos] !=null){
 82                 node = node.sonNode[pos];
 83             }else{
 84                 return false;
 85             }
 86         }
 87         return node.isEnd;
 88     }
 89     
 90     //前序遍历字典树
 91     public void preTraverse(TrieNode node){
 92         if(node != null){
 93             System.out.print(node.val + "-");
 94             for(TrieNode child : node.sonNode){
 95                 preTraverse(child);
 96             }
 97         }
 98     }
 99     
100     //获取根节点
101     public TrieNode getRoot(){
102         return this.root;
103     }
104     
105     //测试
106     public static void main(String[] args) {
107         //构造字典树
108         Trie tree = new Trie();
109         String[] strs = {"banana","band","bee","absolute","acm"};
110         String[] prefix = {"ba","b","band","abc"};
111         for(String string : strs){
112             tree.insert(string);
113         }
114         
115         System.out.println("prefix :" + tree.has("abc"));
116         System.out.println("prefix :" + tree.has("band"));
117         System.out.println("-------------");
118         tree.preTraverse(tree.getRoot());
119         System.out.println("\n-------------");
120         for(String pre: prefix){
121             int num = tree.countPrefix(pre);
122             System.out.println(pre + " -> " + num);
123         }
124         
125     }
126     
127 }