leetcode-208. 实现 Trie (前缀树)

208. 实现 Trie (前缀树)

class Trie {
    private Trie[] children;
    private boolean isEnd;
    /** Initialize your data structure here. */
    public Trie() {
        children = new Trie[26];
        isEnd = false;
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        Trie node = this;
        for (int i = 0; i < word.length(); i++) {
            char ch = word.charAt(i);
            int idx = ch - 'a';
            if (node.children[idx] == null) {
                node.children[idx] = new Trie();
            }
            node = node.children[idx];
        }
        node.isEnd = true;
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        Trie node = this;
        for(int i = 0; i < word.length(); i++){
            char ch = word.charAt(i);
            int idx = ch - 'a';
            if (node.children[idx] == null) {
                return false;
            }
            node = node.children[idx];
        }
        return node.isEnd;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        Trie node = this;
        for(int i = 0; i < prefix.length(); i++){
            char ch = prefix.charAt(i);
            int idx = ch - 'a';
            if (node.children[idx] == null) {
                return false;
            }
            node = node.children[idx];
        }
        return true;
    }
}