Trie Tree的构建 -- find/search/searchAll/search Prefix

比如网上一个例子

一组单词，inn, int, at, age, adv, ant, 我们可以得到下面的Trie：

这里的节点上存的是一个单词，实际上，每个节点走过的路径就是该节点代表的单词.

下面这个链接 对Trie tree 比较好的code 模板，针对leetcode 的： 

https://www.programcreek.com/2014/05/leetcode-implement-trie-prefix-tree-java/

 TrieTree Node 定义有两种形式

1. 如果只包含 a-z的字母

class TrieNode{
    char c;
    TrieNode[] children;
    boolean isLeaf;
    TrieNode(){
        children = new TrieNode[26];
    }
}

2. 如果定义个一个通用性的模板：

class TrieNode{
    char c;
    Map<Character, TrieNode> children;
    boolean isLeaf;
    TrieNode(){
        children = new HashMap<>();
    }
}

一个完整的Trie Tree 模板， 包含了测试程序， 测试过208. Implement Trie (Prefix Tree)/ 425. Word Squares 这道 backtracking + trie解法的题。 

  1 // "static void main" must be defined in a public class.
  2 public class Main {
  3     public static void main(String[] args) {
  4         System.out.println("Hello World!");
  5         Trie trie = new Trie();
  6         trie.insert("apple");
  7         trie.insert("appde");
  8         trie.insert("app");
  9         trie.insert("appxxxx");
 10         trie.insert("epe");
 11        // trie.searchAll("apee");
 12 
 13         System.out.println(trie.searchAll(""));
 14     }
 15 }
 16 
 17 class Trie {
 18 
 19     /** Initialize your data structure here. */
 20     TrieNode root;
 21     public Trie() {
 22         root = new TrieNode(); 
 23     }
 24     
 25     /** Inserts a word into the trie. */
 26     public void insert(String word) {
 27         TrieNode p = root;
 28         for(int i=0; i<word.length(); i++){
 29             char c = word.charAt(i);
 30             if(p.children[c-'a'] != null){
 31                 p = p.children[c-'a'];
 32             }
 33             else {
 34                 TrieNode node = new TrieNode(c);
 35                 p.children[c-'a'] = node;
 36                 p = node;
 37             }
 38             if(i == word.length()-1){
 39                 p.isLeaf = true;
 40             }
 41         }
 42         
 43     }
 44     
 45     /** Returns if the word is in the trie. */
 46     public boolean search(String word) {
 47         TrieNode p = searchNode(word);
 48         if(p!=null && p.isLeaf == true) return true;
 49         return false;
 50         
 51     }
 52     
 53     /** Returns if there is any word in the trie that starts with the given prefix. */
 54     public boolean startsWith(String prefix) {
 55         TrieNode p = searchNode(prefix);
 56         return p != null;
 57     }
 58     
 59     public List<String> searchAll(String prefix){
 60         TrieNode p = searchNode(prefix);
 61         List<String> result = new ArrayList<>();
 62         if(p == null) return result;
 63         preOrder(p, result, prefix);
 64         return result;
 65     }
 66        
 67     private void preOrder(TrieNode root, List<String> result, String curResult){
 68         if(root.isLeaf) {
 69             result.add(curResult.toString());
 70         }
 71         
 72         for(int i=0; i<root.children.length; i++){
 73             //curResult.append(root.children[i].c)
 74             if(root.children[i] != null){
 75                 //curResult.append(root.children[i].c);
 76                 String tmp = curResult + root.children[i].c ;
 77                 preOrder(root.children[i],result,tmp);
 78             }
 79         }
 80     }
 81     
 82     private TrieNode searchNode(String str){
 83         TrieNode p = root;
 84         for(int i=0; i<str.length(); i++){
 85             char c = str.charAt(i);
 86             if(p.children[c-'a'] == null) return null;
 87             else {
 88                 p = p.children[c-'a'];
 89             }
 90         }
 91         
 92         return p;
 93     }
 94     
 95     class TrieNode{
 96         char c;
 97         TrieNode[] children;
 98         boolean isLeaf;
 99         TrieNode(){
100             children = new TrieNode[26];
101         }
102         TrieNode(char c){
103             this.c = c;
104             children = new TrieNode[26];
105         }
106     }
107 }