题目
Implement a trie with insert, search, and startsWith methods.

Note:
You may assume that all inputs are consist of lowercase letters a-z.

答案

class Trie {

    class TrieNode {
        // Initialize your data structure here.
        public TrieNode() {
            children = new TrieNode[26];
            bLeaf = false;
        }
        int value;
        boolean bLeaf;
        TrieNode[] children;
    }

    private boolean charExist(char c, TrieNode curr) {
        return curr.children[c - 'a'] != null;
    }
    private TrieNode nextNode(char c, TrieNode curr) {
        return curr.children[c - 'a'];
    }
    private void insertChar(char c, TrieNode curr, TrieNode ins) {
        curr.children[c - 'a'] = ins;
    }

    
    TrieNode root;
    /** Initialize your data structure here. */
    public Trie() {
        root = new TrieNode();
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        TrieNode curr = root;
        for(int i = 0; i < word.length(); i++) {
            char c = word.charAt(i);
            if(!charExist(c, curr)) {
                TrieNode newnode = new TrieNode();
                newnode.value = c;
                insertChar(c, curr, newnode);                
            }
            // You will need to mark this node as leaf, even if it is not really a leaf in the tree
            // but it is a leaf for this particular string word
            
            curr = nextNode(c, curr);
            if(i == word.length() - 1)
                curr.bLeaf = true;
        }
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode curr = root;
        for(int i = 0; i < word.length(); i++) {
            char c = word.charAt(i);
            if(charExist(c, curr))
                curr = nextNode(c, curr);
            else
                return false;
        }
        return curr.bLeaf;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        TrieNode curr = root;
        for(int i = 0; i < prefix.length(); i++) {
            char c = prefix.charAt(i);
            if(charExist(c, curr))
                curr = nextNode(c, curr);
            else
                return false;
        }
        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);
 */