LeetCode-208.Implement Trie(Prefix Tree)

Implement a trie with insert, search, and startsWith methods.

Example:

Trie trie = new Trie();

trie.insert("apple");
trie.search("apple");   // returns true
trie.search("app");     // returns false
trie.startsWith("app"); // returns true
trie.insert("app");   
trie.search("app");     // returns true

Note:

• You may assume that all inputs are consist of lowercase letters a-z.
• All inputs are guaranteed to be non-empty strings.

使用数组保存子节点，但是不可扩展，效率高

使用ArrayList保存子节点，可扩展，但查找效率差

使用Map保存子节点

class Trie {// mytip
    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;
        if(null==cur){
            cur = new TrieNode();
        }
        for (int i = 0; i < word.length(); i++) {
            char c = word.charAt(i);
            List<TrieNode> list = cur.children;
            boolean flag = false;
            for (int j = 0; j < list.size() ; j++) {
                if(list.get(j).val==c){
                    cur = list.get(j);
                    flag = true;
                    break;
                }
            }
            if(!flag){
                TrieNode t = new TrieNode(c);
                cur.children.add(t);
                cur = t;
            }
        }
        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(null==cur||null==cur.children||0==cur.children.size()){
                return false;
            }
            List<TrieNode> list = cur.children;
            boolean flag = false;
            for (int j = 0; j < list.size() ; j++) {
                if(list.get(j).val==c){
                    cur = list.get(j);
                    flag =true;
                    break;
                }
            }
            if(!flag){
                return false;
            }
        }
        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(null==cur||null==cur.children||0==cur.children.size()){
                return false;
            }
            List<TrieNode> list = cur.children;
            boolean flag = false;
            for (int j = 0; j < list.size() ; j++) {
                if(list.get(j).val==c){
                    cur = list.get(j);
                    flag =true;
                    break;
                }
            }
            if(!flag){
                return false;
            }
        }
        return true;
    }
}

class TrieNode{
    List<TrieNode> children;//孩子结点使用List存放 效率较低
    char val;
    boolean isWord;
    TrieNode(){
        children = new ArrayList<>();
        isWord = false;
    }
    TrieNode(char c){
        children = new ArrayList<>();
        isWord = false;
        val =c;
    }
}

class Trie {//my
    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;
        if(null==cur){
            cur = new TrieNode();
        }
        for (int i = 0; i < word.length(); i++) {
            char c = word.charAt(i);
            Map<Character,TrieNode> list = cur.children;
            if(list.containsKey(c)){
                cur = list.get(c);
            }
            else{
                TrieNode t = new TrieNode(c);
                cur.children.put(c,t);
                cur = t;
            }
        }
        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(null==cur||null==cur.children||0==cur.children.size()){
                return false;
            }
            Map<Character,TrieNode> list = cur.children;
            if(list.containsKey(c)){
                cur = list.get(c);
            }
            else{
                return false;
            }
        }
        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(null==cur||null==cur.children||0==cur.children.size()){
                return false;
            }
            Map<Character,TrieNode> list = cur.children;
            if(list.containsKey(c)){
                cur = list.get(c);
            }
            else{
                return false;
            }
        }
        return true;
    }
}

class TrieNode{
    Map<Character,TrieNode> children;//使用map存放子节点
    char val;
    boolean isWord;
    TrieNode(){
        children = new HashMap<>();
        isWord = false;
    }
    TrieNode(char c){
        children = new HashMap<>();
        isWord = false;
        val =c;
    }
}

进阶题

单词搜索 LeetCode212 https://www.cnblogs.com/zhacai/p/10641592.html