前缀树(字典树)trieTree两种实现

实现TrieTree中的易混淆的地方：注意查找字符串和字符串前缀的区别
1.查找字符串的话,要使用最后一个节点判断是否为单词,多种解决办法,可以设置标志位,tree：单词，false：不是单词，是字串的中间部分
或者也可以用第一种实现中的end值，end>0表示字符串结尾
2.查找前缀的话,没条件,只要trietree中有前缀单词即可

最后标注:数据结构的实现是多种多样的,掌握核心的灵魂才是关键

数组实现trieTree:缺点浪费空间,一般不使用

public class TrieTree {
    //trietree主要应用于字符串查找
    // trieTree node
    class Node{
        int pass;
        int end;
        Node[] next;
        public Node(){
            pass = 0;
            end = 0;
            next = new Node[26];
        }
    }
    Node root;
    // init trienode
    public TrieTree(){
        root = new Node();
    }
    // insert the string,this is create the trietree
    public void insert(String word){
        if (word == null)
            return;
        char[] chars = word.toCharArray();
        Node node = root;
        node.pass++;
        for (int i = 0; i < chars.length; i++) {
            int index = chars[i] - 'a';
            if (node.next[index] == null){
                node.next[index] = new Node();
            }
            node = node.next[index];
            node.pass++;
        }
        node.end++;
    }
    // search the count of the word in the trietree
    public int search(String word){
        if (word == null)
            return 0;
        Node node = root;
        char[] chars = word.toCharArray();
        for (int i = 0; i < chars.length; i++) {
            int index = chars[i] - 'a';
            // don't exits the word
            if (node.next[index] == null)
                return 0;
            node = node.next[index];
        }
        //判断查找前缀和查找字符串区别:查找单词得看结尾节点的end值,查找前缀不需要
        return node.end;
    }
    // search the count of prefix of the word
    public int prefixWord(String word){
        if (word == null)
            return 0;
        char[] chars = word.toCharArray();
        Node node = root;
        for (int i = 0; i < chars.length; i++) {
            int index = chars[i] - 'a';
            if (node.next[index] == null)
                return node.pass;
            node = node.next[index];
        }
        return node.pass;
    }
    // delete the string of the word
    // two condition:one just end,two has ends characters,这里仅仅删除一个字符串,想要删除多个,可以修改代码循环判断search(word)==0?,达到删除所有word的目的
    public boolean delete(String word){
        if (search(word) == 0)
            return false;
        Node node = root;
        node.pass--;
        char[] chars = word.toCharArray();
        for (int i = 0; i < chars.length; i++) {
            int index = chars[i] - 'a';
            if (--node.next[index].pass == 0){
                node.next[index] = null;
                return false;
            }
            node = node.next[index];
        }
        node.end--;
        return true;
    }
}

字典实现trieTree：优点:灵活可以随机设置,节省空间,推荐使用

class Trie {
    /**
     * trietree主要应用于字符串查找
     * 判断查找前缀和查找字符串区别:
     * 查找单词得看结尾节点的end值,查找前缀不需要,
     * 或者可以设一个标志位判断是字符还是前缀
     */
    class TrieNode {
        public boolean isWord;
        public Map<Character, TrieNode> childrenMap = new HashMap<>();
    }

    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 cur = root;
        for(int i = 0; i < word.length(); i++){
            char c = word.charAt(i);
            if(cur.childrenMap.get(c) == null){
                // insert a new node if the path does not exist
                cur.childrenMap.put(c, new TrieNode());
            }
            cur = cur.childrenMap.get(c);
        }
        cur.isWord = true;
    }

    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode cur = root;
        for(int i = 0; i < word.length(); i++) {
            char c = word.charAt(i);
            if(cur.childrenMap.get(c) == null) {
                return false;
            }
            cur = cur.childrenMap.get(c);
        }
        return cur.isWord;
    }

    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        TrieNode cur = root;
        for(int i = 0;i < prefix.length(); i++){
            char c = prefix.charAt(i);
            if(cur.childrenMap.get(c) == null) {
                return false;
            }
            cur = cur.childrenMap.get(c);
        }
        return true;
    }
}