Implement Trie (Prefix Tree) 两种实现方法的比较

class TrieNode {
    public TrieNode[] children = new TrieNode[26];
    public String item = "";  

    // Initialize your data structure here.
    public TrieNode() {
    }
}  

class Trie {
    private TrieNode root;  

    public Trie() {
        root = new TrieNode();
    }  

    // Inserts a word into the trie.
    public void insert(String word) {
        TrieNode node = root;
        for (char c : word.toCharArray()) {
            if (node.children[c - ‘a‘] == null) {
                node.children[c - ‘a‘] = new TrieNode();
            }
            node = node.children[c - ‘a‘];
        }
        node.item = word;
    }  

    // Returns if the word is in the trie.
    public boolean search(String word) {
        TrieNode node = root;
        for (char c : word.toCharArray()) {
            if (node.children[c - ‘a‘] == null) return false;
            node = node.children[c - ‘a‘];
        }
        return node.item.equals(word);
    }  

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    public boolean startsWith(String prefix) {
        TrieNode node = root;
        for (char c : prefix.toCharArray()) {
            if (node.children[c - ‘a‘] == null) return false;
            node = node.children[c - ‘a‘];
        }
        return true;
    }
}  

class TrieNode {
    // Initialize your data structure here.
    char c;
    boolean leaf;   //leaf属性是一个字符串的结尾标志
    HashMap<Character, TrieNode> children = new HashMap<Character, TrieNode>();  

    public TrieNode(char c) {
        this.c = c;
    }  

    public TrieNode(){};
}  

class Trie {
    private TrieNode root;  

    public Trie() {
        root = new TrieNode();
    }  

    // Inserts a word into the trie.
    public void insert(String word) {
        Map<Character, TrieNode> children = root.children;   //用map构造了一个trie树
        for(int i=0; i<word.length(); i++) {
            char c = word.charAt(i);
            TrieNode t;
            if(children.containsKey(c)) {
                t = children.get(c);
            } else {
                t = new TrieNode(c);
                children.put(c, t);
            }
            children = t.children;
            if(i==word.length()-1) t.leaf=true;
        }
    }  

    // Returns if the word is in the trie.
    public boolean search(String word) {
        TrieNode t = searchNode(word);
        return t!=null && t.leaf;
    }  

    public boolean startsWith(String prefix) {
        return searchNode(prefix) != null;
    }  

    private TrieNode searchNode(String word) {
        Map<Character, TrieNode> children = root.children;
        TrieNode t = null;
        for(int i=0; i<word.length(); i++) {
            char c = word.charAt(i);
            if(!children.containsKey(c)) return null;
            t = children.get(c);
            children = t.children;
        }
        return t;
    }
}