算法专题之字典树

转载自 https://leetcode-cn.com/problems/implement-trie-prefix-tree/solution/shi-xian-trie-qian-zhui-shu-by-leetcode/

什么是字典树/前缀树

灵魂画手233！！！！

字典树的crud操作的算法实现

class Trie {
    private TrieNode root;
    class TrieNode {

    // R links to node children
    private TrieNode[] links;

    private final int R = 26;

    private boolean isEnd;

    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 void setEnd() {
        isEnd = true;
    }
    public boolean isEnd() {
        return isEnd;
    }
   }
    //以上是构建字典树的节点
    /** Initialize your data structure here. */
    public Trie() {
        root = new TrieNode();
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
         TrieNode node = root;
        for (int i = 0; i < word.length(); i++) {
            char currentChar = word.charAt(i);
            if (!node.containsKey(currentChar)) {
                node.put(currentChar, new TrieNode());
            }
            node = node.get(currentChar);
        }
        node.setEnd();
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode node = searchPrefix(word);
       return node != null && node.isEnd();
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
         TrieNode node = searchPrefix(prefix);
        return node != null;
    }


     // search a prefix or whole key in trie and
    // returns the node where search ends
    private TrieNode searchPrefix(String word) {
        TrieNode node = root;
        for (int i = 0; i < word.length(); i++) {
           char curLetter = word.charAt(i);
           if (node.containsKey(curLetter)) {
               node = node.get(curLetter);
           } else {
               return null;
           }
        }
        return node;
    }
}

/**
 * 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);
 */

练习题

public class WordDictionary {

    class Node {
        private Node[] next;
        private boolean isWord;

        public Node() {
            next = new Node[26];
            isWord = false;
        }
    }

    private Node root;

    /**
     * Initialize your data structure here.
     */
    public WordDictionary3() {
        root = new Node();
    }

    /**
     * Adds a word into the data structure.
     */
    public void addWord(String word) {
        int len = word.length();
        Node curNode = root;
        for (int i = 0; i < len; i++) {
            char curChar = word.charAt(i);
            Node next = curNode.next[curChar - 'a'];
            if (next == null) {
                curNode.next[curChar - 'a'] = new Node();
            }
            curNode = curNode.next[curChar - 'a'];
        }
        if (!curNode.isWord) {
            curNode.isWord = true;
        }
    }

    /**
     * Returns if the word is in the data structure. A word could contain the dot character '.' to represent any one letter.
     */
    public boolean search(String word) {
        return match(word, root, 0);
    }

    private boolean match(String word, Node node, int start) {
        if (start == word.length()) {
            return node.isWord;
        }
        char alpha = word.charAt(start);
        if (alpha == '.') {
            for (int i = 0; i < 26; i++) {
                if (node.next[i] != null && match(word, node.next[i], start + 1)) {
                    return true;
                }
            }
            return false;
        } else {
            if (node.next[alpha - 'a'] == null) {
                return false;

            }
            return match(word, node.next[alpha - 'a'], start + 1);
        }
    }
}

数组中两个数的最大异或值