前缀树(Trie)

实现前缀树

知识点

Trie (发音为 "try") 或前缀树是一种树数据结构，用于检索字符串数据集中的键。
常见的应用场景有：

• 自动补全
• 拼写检查
• IP路由（最长前缀匹配）
• 打字预测

示例

208. 实现 Trie (前缀树)

class TrieNode {
    private final int R = 26;
    private TrieNode[] links;
    private boolean isEnd = false;

    public TrieNode() {
        links = new TrieNode[R];
    }

    public boolean containsKey(char ch) {
        return links[ch-'a'] != null;
    }

    public TrieNode get(char ch) {
        return links[ch-'a'];
    }

    public void put(char ch, TrieNode node) {
        links[ch-'a']=node;
    }

    public boolean isEnd() {
        return isEnd;
    }

    public void setEnd() {
        isEnd = true;
    }
}

class Trie {
    private TrieNode root;

    /** Initialize your data structure here. */
    public Trie() {
        root = new TrieNode();
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        TrieNode node = root;
        char[] charArray = word.toCharArray();
        int len = charArray.length;
        for (int i=0;i<len;i++) {
            if (!node.containsKey(charArray[i])) {
                node.put(charArray[i], new TrieNode());
            }
            node=node.get(charArray[i]);
        }

        node.setEnd();
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode node = root;
        char[] charArray = word.toCharArray();
        int len = charArray.length;
        for (int i=0;i<len;i++) {
            if (!node.containsKey(charArray[i])) {
                return false;
            }
            node=node.get(charArray[i]);
        }

        return node.isEnd();
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        TrieNode node = root;
        char[] charArray = prefix.toCharArray();
        int len = charArray.length;
        for (int i=0;i<len;i++) {
            if (!node.containsKey(charArray[i])) {
                return false;
            }
            node=node.get(charArray[i]);
        }

        return true;
    }
}