leetcode刷题（55）——208. 实现 Trie (前缀树)

Trie trie = new Trie();

trie.insert("apple");
trie.search("apple");   // 返回 true
trie.search("app");     // 返回 false
trie.startsWith("app"); // 返回 true
trie.insert("app");   
trie.search("app");     // 返回 true

class Trie {

    class TreeNode{
        char val;
        TreeNode[] treeSet = new TreeNode[26];
        boolean isEndWord = false;
        TreeNode(char c){
            val = c;
        }
    }

    private TreeNode root;
    /** Initialize your data structure here. */
    public Trie() {
        root = new TreeNode(' ');
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        TreeNode ws = root;
        for(int i=0;i<word.length();i++){
            char c = word.charAt(i);
            if(ws.treeSet[c-'a']==null){
                ws.treeSet[c-'a'] = new TreeNode(c);
            }
            ws=ws.treeSet[c-'a'];
        }
        ws.isEndWord = true;
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TreeNode ws = root;
        for(int i=0;i<word.length();i++){
            char c = word.charAt(i);
             if(ws.treeSet[c-'a']==null){
                return false;
            }
           ws= ws.treeSet[c-'a'];
        }
        return ws.isEndWord;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        TreeNode ws = root;
        for(int i=0;i < prefix.length();i++){
            char c = prefix.charAt(i);
             if(ws.treeSet[c-'a']==null){
                return false;
            }
           ws= ws.treeSet[c-'a'];
        }
        return true;
    }
}

/**
 * Your Trie object will be instantiated and called as such:
 * Trie obj = new Trie();
 * obj.insert(word);
 * boolean param_2 = obj.search(word);
 * boolean param_3 = obj.startsWith(prefix);
 */